Thoughts on counterfactual reasoning

These examples of counterfactuals are presented as equivalent, but they seem meaningfully distinct:

What if the sun suddenly went out?
What if 2+2=3?

Specifically, they don't seem equally difficult for me to evaluate. I can easily imagine the sun going out, but I'm not even sure what it would mean if 2+2=3. It confuses me that these two different examples are presented as equivalent, because they seem to be instances of meaningfully distinct classes of something. I spent some time trying to characterize why the sun example is intuitively easy for me and the math example is intuitively difficult for me. I came up with some ideas, but I won't go into details yet because they seem like the obvious sorts of things that anyone who has read The Sequences (a.k.a., Rationality: A-Z) would have thought of. I strongly suspect there's prior work. It is also possible that I don't fully understand the problem yet.

The two counterfactual reasoning examples above (and others) are presented as equivalent, but they seem like they are not.

1. Is this an intentional simplification for the benefit of new readers?

2. If so, can someone point me to the prior work exploring the omitted nuances of counterfactuals? I don't want to re-invent the wheel.

3. If not, would exploration of the characteristics of different kinds of counterfactuals be a fruitful area of research?