My advice is don't stress too much about labels. 

I'm a woman who dates in kink-adjacent circles, and I'm a dommy switch so I have seen a lot of subby guys' profiles. You seem pretty normal, you seem like the sort of guy I date, down to the social awkwardness/lack of experience. I have a goddess kink so your specific fantasy is right up my alley. There are lots of women like me.

I've dated men who have been pretty normal but just didn't enjoy vaginal sex, we still had sex but just not PIV. I've dated men with fetishes who also enjoyed sex. 

If you WANT some labels, the different types of attraction might speak to you:

https://lgbtq.unc.edu/resources/exploring-identities/asexuality-attraction-and-romantic-orientation/ 

As you said about the painting, it may be that you are attracted to women in an aesthetic way. 

The good thing about labels is that people don't generally police them too hard because they're never perfect; I myself identify as straight but it's not a perfect label for me, just very very close. 

If it makes you happy to call yourself asexual or demisexual or whatever, then do it, try it on. You can always change your mind later. Maybe try joining local ace groups and talking about your experience with them, or reading through relevant subreddits.

It might be helpful to think about sexuality as a set of sliders or volume knobs. Sounds like your desire for partner sex is set pretty low, but your romantic desire is set higher. The two don't necessarily correlate the way the culture tends to suggest [1]. Those settings would fall into the asexual part of the variable space, but not the aromantic part. Likewise, it sounds like you have non-negative feelings toward sex in general, so you probably aren't "sex repulsed" like some asexuals.

Regarding the power fantasies, remember that fantasies are tricky things. They don't always represent something we would or could do in real life. And the particular psychological itch that a fantasy scratches doesn't have to be about the sex, even if you're having fantasies where sex is going on. Could be exclusively the social dynamic that's really doing it for you there.

[^1] This is the part it seems like your doctor has forgotten: we can be attracted, even strongly attracted to someone for reasons other than sexual desire!

What's going on? Is this a thing any other people feel? Is there a term for this? Is this some kind of niche asexuality? Am I actually just a regular heterosexual guy that just needs to have good sex to realize how much I actually do want it?

After puzzling over almost an identical experience to what you’ve described, I’ve concluded that human sexuality is an experience for which existing language is woefully unequipped. This is extremely frustrating in some regards, because it seems like a proper label or diagnosis would be the most useful for learning more and connecting with others who share your experience. If you can figure out what’s “wrong” with you, then you can start to look for answers to fix it.

In all likelihood, though, a perfect diagnosis doesn’t exist. You might find that labels like “asexual”, or sub-classifications such as “grey” or “demi” ace apply to your experience, but these terms are also quite broad and you’ll discover they describe a range of experiences which sometimes apply to you and frequently do not. There are also undoubtedly parts of your experience (like your strong visual attraction to the opposite gender) which don’t fit the mold and are confusing (even to experts), sometimes threatening to “break” the diagnosis entirely.

As frustrating as this may be, this understanding of the limitations of our language has the potential to be liberating because it indicates that existing labels are too rigid. Note that I’m not advocating for a nihilistic lack of definition, because that’s probably not going to be satisfying to you. (Although if it is, then know that with all I’ve said, this is a perfectly legitimate position to take.) Instead, consider an alternative in which you have immense freedom to mix and match the individual components of these labels (or augment them with your own innovations where necessary) until you arrive at something that you feel approximates “you.” It won’t ever be perfectly accurate or even necessarily fit into a neat sound byte, but that’s okay — our identities are much more complex than a few words can ever fully capture.

Also, don’t be afraid to simply try out labels that catch your attention (or pieces of them) like they’re clothing. Playing around with identity can be scary at first because it seems like such a Big Step in accepting that you might really be “different.” It’s tough to offer any consolation, except that it gets easier as you do it more and start to see how easily you can always try on something else if what you’re wearing doesn’t fit right. You don’t have to inform anyone regarding these updates if you don’t want to, by the way, although note that it can be helpful and encouraging if you can confide in a close friend with an open mind.

I’d also like to address your final question because it reminds me of a suspicion of, “Am I actually normal and my biological drives are just temporarily miscalibrated?” I’ve had this thought before, and before I take a stab at it directly, I’d like to offer a (perhaps untair) analogy for what it sounds similar to. “You said you’re gay, but maybe you just haven’t been with a real woman.” I realize this isn’t entirely the same, because your mix of observations would be more akin to a gay man noticing that, while he likes sex with other men, he stares almost exclusively at women. (Hey, look! Another set of observations which break the mold — of course, if you break the mold frequently and in large enough numbers for people to notice, they might just make a new label: in this case, “bisexual”.) So now for the longer reply:

It’s entirely possible that you need a “reset”. At the same time, this hasn’t been my experience, nor would I advise treating yours as such. Everyone has preferences in taste, whether that’s food or art or women or sex, and that’s perfectly fine. The same way that tasting the most luxurious chocolate won’t make you enjoy it if you hate cocoa; or hearing John Coltrane won’t convert you to jazz if you hate jazz… there isn’t some magical experience with a woman that’s going to “fix” you or make you realize how much you “need” some good, old-fashioned sex. Maybe you don’t need or want sex in a physical way. Maybe you find women attractive from a distance. Yet maybe, to top the puzzle off, you still want a partner who will dominate you, although the idea that gets you off isn’t her as much as the power dynamic, and at the same time you’re still into her and the idea of being in an exclusive relationship where you cuddle and show your affection and the sex isn’t as big a deal. I’m not going to lie and say you’re in the majority, but you also wouldn’t be the first person to feel this way.

Unfortunately, I suspect that a decent amount of “figuring this out” will come from lived experience, by which I mean experiments with the opposite sex and with sex/intimacy. You can fantasize and concoct thought experiments to see what turns you on and use that as a basic guide, but ultimately nothing will tell you what works for you in the same way as running the experiment will. Odds are, you learned a lot about what you liked / didn’t like from even a simple make-out session, and there’s no substitute for figuring out your preferences via contact with the real world.

With regard to how to run these experiments, I’d like to point out that dating and asexuality / atypical sex preference (of whatever flavor) are entirely compatible. It’s not as easy as defaulting to the “norm” in relationships, but it is possible if you consider that relationships are about far more than just sex. As an example, many women either don’t orgasm from PIV sex alone; or can’t orgasm without aid of toys / fingers / etc; and some don’t even orgasm or find orgasm to be pleasurable, and would rather focus on their partner. It seems strange that this openness to variability would be accepted for women, yet not for men. I’ve chatted (online) with a number of people on both sides of ace relationships (some consisting of highly sex-repulsed individuals), and sex is either a small part of the relationship or else is performed with suitable modifications or alternatives. In the end, communication is the key, and the right person will be willing and able to explore with you safely and securely to find what works for both of you.

I’m glad you asked about this and I wish you luck on the journey of self discovery! If you have any questions, feel free to DM me.

Sounds like you've imprinted some sort of not exactly resentment+rejection of the power+value of female sexuality (as I think some gay men have) but rather frustrated worship+submission to it, congruent with high porn consumption, although you say you don't actually consume much since the out and about the powerless man ogling/frustration stimulus is enough. 
This voyeurish mode and esp. the powerlessness arousal fetish doesn't help you pose as the typically high-value 'prize' so the lack of access isn't surprising. As an unsolicited prescription, I'd suggest getting used to interacting with as high-value women as you can stand as powerfully as possible (even if that mean just not acting thirsty; confident flirtation/approaches are even better). If your desire were more connected to pursuit you'd learn+calibrate as part of a road to increasing comfort and inevitably results.

Between your lack of interest in sex generally (and vaginal intercourse specifically) and your preference to be dominated, you don't sound like a regular heterosexual male to me (where "regular" is strictly defined by the mode and everything else counts as niche) but your desire (as a man) to be dominated by a woman is a well-established niche, as evidenced by the dominatrix industry (though dominatrices are often associated with BDSM), female dominance hentai and countless other things on the Internet.

Whether you quality as asexual sounds like an discussion about words and not what they're pointing to.