The answer from Quora stating that it had to do with different skill sets is completely ignorant of modern day military practices. For instance, Master Chiefs in the navy, especially once they get the specific qualification tailored to their department, don't stand watch and are completely managerial in nature. You will never see a Master chief do any sort of labor intensive job unless they are breaking the rules. This is even true in combat units where high ranking enlisted Navy SEALs generally default to desk jobs just like their officer counterparts. This is not always true, but it's most often true. This transfer takes place as you increase in rank and you'll start seeing the beginnings of it as low as E-5 in some branches, higher in others.
The only true difference is that officer deployment rotations generally have them doing more than just their main job. For instance, a nuclear officer will also be an officer on non-nuclear ships for certain tours. So while a Master Chief will be doing the same job as a O-1 to O-3, he will always do it within the same department or same type of department - with exception to Washington jobs. While the overall titles are different the concept of the jobs are the same.
For example:
A Division Master Chief, deals with personnel and divisional duties while a Divisional Officer deals more with personnel and to a lesser extent with divisional duties, but still signs off on schedules.
A Department Master Chief deals almost exclusively with personnel and has very little to do with maintenance or Departmental duties - their only real involvement in departmental duties is related to personnel use. A Division Head (usually an O-4 or O-5) deals heavily in Divisional duties and schedules.
As far as actual "watches" go, or "shifts," the E-7 to O-3 can all have the same shifts with exception to a few, in some fields.
Still, when it comes down to it, you have a situation where senior enlisted are basically doing the same job as a O-1 to O-3, getting paid more until the officer gets to O-3 (which is basically given to officers in many fields as long as they are somewhat competent). Generally, this is explained with the purpose of having highly seasoned knowledgeable enlisted, guiding the junior officers so that they can become knowledgeable senior officers. So we are training the officers on how to be officers, using the people that are incapable of being officers because they have an "E" in front of their rank. If officers were a specific breed, the officers would train the officers, period. And it's not that they are just being trained on a technical level, they are being trained on a managerial level, if that was a rebuttal. Also, even if an enlisted person does switch to a commission, they have to deal with belittlement due to the fact that they are "dirty" or a "lesser form of an officer." True, there have been enlisted who have made it to the very top of the officer chain, but they are far and few between with most getting locked at an O-4/O-5 level, mostly due to discrimination. Most of the discrimination is indirect - enlisted are rarely nurtured to be officers. In fact, it usually hurts their department to lose a body, so they won't encourage it. Some of it is direct with Adm Boorda as an example. Sure, he was also discriminated against for getting tough with sexism in the Navy, but no Chief of Naval operations has been so unpopular as he was, even at the highest levels, and even prior to the scandal over awards.
I think the true issue with switching to a one ladder system is pay, as I touched on before. Even if you made master chief in 10 years (which is extremely rare) - the problem increases with more time in service - you would still lose pay if you then got promoted to O-1 even if you use the "prior enlisted" officer pay. You'd either have to lower the upper end of enlisted pay or raise the lower end of officer pay, both of which have consequences.
Maybe a solution would be lowering specialist bonuses and using that to raise officer pay. However, the Navy, in particular, is already having serious issues in getting quality bodies for it's higher education positions such as nuclear officers and enlisted. Even better, you could get rid of E-7 to E-9 and make them all officers.
At the same time, you'd have to change the way officers work. Generally, they keep officers moving to gain experience in different areas of the Navy and to reduce chances of a turncoat army. They would have to still have specialists higher up, so there would have to be non-managerial tech rates for officers, such as warrant officers who, by-the-way, already exist and would have to be maintained and expanded.
As a side note, most people who compare enlisted to officers, seem to be using the lower E-1 to E-4 as an example of enlisted with like full birds as their example of officers. Yes, E-4 and below generally consist of high school kids with very little life experience, but the morph into one ladder would have you compare the higher enlisted (E-7 to E-9) to junior officers and in reality, there is no difference other than... you have to solute one.
The answer from Quora stating that it had to do with different skill sets is completely ignorant of modern day military practices. For instance, Master Chiefs in the navy, especially once they get the specific qualification tailored to their department, don't stand watch and are completely managerial in nature. You will never see a Master chief do any sort of labor intensive job unless they are breaking the rules. This is even true in combat units where high ranking enlisted Navy SEALs generally default to desk jobs just like their officer counterparts. This is not always true, but it's most often true. This transfer takes place as you increase in rank and you'll start seeing the beginnings of it as low as E-5 in some branches, higher in others.
The only true difference is that officer deployment rotations generally have them doing more than just their main job. For instance, a nuclear officer will also be an officer on non-nuclear ships for certain tours. So while a Master Chief will be doing the same job as a O-1 to O-3, he will always do it within the same department or same type of department - with exception to Washington jobs. While the overall titles are different the concept of the jobs are the same. For example:
A Division Master Chief, deals with personnel and divisional duties while a Divisional Officer deals more with personnel and to a lesser extent with divisional duties, but still signs off on schedules.
A Department Master Chief deals almost exclusively with personnel and has very little to do with maintenance or Departmental duties - their only real involvement in departmental duties is related to personnel use. A Division Head (usually an O-4 or O-5) deals heavily in Divisional duties and schedules.
As far as actual "watches" go, or "shifts," the E-7 to O-3 can all have the same shifts with exception to a few, in some fields.
Still, when it comes down to it, you have a situation where senior enlisted are basically doing the same job as a O-1 to O-3, getting paid more until the officer gets to O-3 (which is basically given to officers in many fields as long as they are somewhat competent). Generally, this is explained with the purpose of having highly seasoned knowledgeable enlisted, guiding the junior officers so that they can become knowledgeable senior officers. So we are training the officers on how to be officers, using the people that are incapable of being officers because they have an "E" in front of their rank. If officers were a specific breed, the officers would train the officers, period. And it's not that they are just being trained on a technical level, they are being trained on a managerial level, if that was a rebuttal. Also, even if an enlisted person does switch to a commission, they have to deal with belittlement due to the fact that they are "dirty" or a "lesser form of an officer." True, there have been enlisted who have made it to the very top of the officer chain, but they are far and few between with most getting locked at an O-4/O-5 level, mostly due to discrimination. Most of the discrimination is indirect - enlisted are rarely nurtured to be officers. In fact, it usually hurts their department to lose a body, so they won't encourage it. Some of it is direct with Adm Boorda as an example. Sure, he was also discriminated against for getting tough with sexism in the Navy, but no Chief of Naval operations has been so unpopular as he was, even at the highest levels, and even prior to the scandal over awards.
I think the true issue with switching to a one ladder system is pay, as I touched on before. Even if you made master chief in 10 years (which is extremely rare) - the problem increases with more time in service - you would still lose pay if you then got promoted to O-1 even if you use the "prior enlisted" officer pay. You'd either have to lower the upper end of enlisted pay or raise the lower end of officer pay, both of which have consequences.
Maybe a solution would be lowering specialist bonuses and using that to raise officer pay. However, the Navy, in particular, is already having serious issues in getting quality bodies for it's higher education positions such as nuclear officers and enlisted. Even better, you could get rid of E-7 to E-9 and make them all officers.
At the same time, you'd have to change the way officers work. Generally, they keep officers moving to gain experience in different areas of the Navy and to reduce chances of a turncoat army. They would have to still have specialists higher up, so there would have to be non-managerial tech rates for officers, such as warrant officers who, by-the-way, already exist and would have to be maintained and expanded.
As a side note, most people who compare enlisted to officers, seem to be using the lower E-1 to E-4 as an example of enlisted with like full birds as their example of officers. Yes, E-4 and below generally consist of high school kids with very little life experience, but the morph into one ladder would have you compare the higher enlisted (E-7 to E-9) to junior officers and in reality, there is no difference other than... you have to solute one.