One simple question, have you ever been penetrated anally in real life or are just theorizing about Amazons and their positions, based on watching too much hentai drawings? Be honest.
Unless one's an anal acrobat with high mileage, receiving a penis in anus is a technique that requires a good deal of preparation and relaxation on the part of the bottom. Extra lubrication is also helpful. Relaxation of the pelvic floor is counterintuitive to active participation in setting the pace or force of the penetration. 99% of the time, you take it up the ass (passively), not give it with the ass (actively), which is different from giving head, where yes, the mouth has much more say on the pace and intensity of the penetration. You used this expression yourself, not even realizing the difference between 'taking' and 'giving' in terms of sexual power exchange.
I've been fisted before, so yeah, I'd say I'm pretty experienced; I'd probably even go so far as to say I've got more experience taking than giving, and that's part of why I'm so confident dominance exists separately from pitching and catching. Ah, and I'm using taking and giving synonymously with pitching and catching there, not denoting movement; I just don't wanna get monotonous using the same phrases all the time. I don't wanna give the wrong idea, so full disclosure, it's only happened twice, and I was using poppers, but it has happened. I've also spent like 3 grand on toys, and some of the ones I have are pretty sizeable, but that's spread out over several years. I mean, that's part of the whole reason I'm a fan of anal in the first place; I like empathizing with the bottom, and I, personally, do not have a vagina. Anal I can copy, vaginal I have to make do and guess what it it would feel like to be fucked in the front butt. And the Amazon position and anal are mostly unrelated, it just shows an example of a position where the pitcher is pretty much always submissive. Someone putting your feet behind your ears makes it harder to be dominant. I mean, I don't think it's mutually exclusive either way; you could be in the amazon position and having anal sex much easier, but I'm sure it would still be possible to manage being dominant as a top in that position. I can't picture it personally, but I'm sure someone could manage it. Even with all of that, you don't have to move an inch to be dominant, even if you're being penetrated. Like pretty much anything else, movement is separate from dominance and submission. Pretty sure I gave an example that already showed that, the monopoly one. If they're giving it their best, and you don't even acknowledge them, that could be very dominant. It could be very submissive too if it was a free use scenario, don't get me wrong, but it's like I was saying, it depends on the situation more than the action. They could be setting the pace, they could decide everything that happens, but you're still the dominant one. If they can do whatever they want and can't even get you to blink, it's hard to say they're dominating you.
You don't need high mileage to take an average dick. Not even close. You need some experience and/or practice, but most dicks just aren't close to porn sized. And by some experience, I just mean not being a virgin, essentially; you don't need to have written books about it. Most people have taken shits bigger than most dicks. They just don't think about it. Now, flesh is a bit more rigid, but size-wise, even after it comes out, you've probably passed bigger things than you'll take most of the time. More than anything else, you just need to not freak out about it. If you're tense and clenching, yeah, you're gonna have a bad time. You do need to relax, but it's just a "don't clench" relax, not an "if there's any tension anywhere in your body you'll rip something or it will never go in" relax. But if you've played with yourself, like at all, 80-90% of human dicks aren't scary. Don't get me wrong, stretching definitely helps, but it's more a minute or two to increase blood flow than hours of stretching for normal situations. If somebody has a monster, it's different, but the average dick size is only like 5-7 inches. Most of the idea that its such a hard thing that takes years of practice to master comes from guys who don't even wash their ass in the shower cause they think touching back there is gay and bad.
While you may find a rare short porn clip with a woman riding a stationary dick with her butt triumphantly, bear in mind that prior to that, that 'Domina' has probably taken an enema or two, wore a buttplug for a while to relax herself and used plenty of lube. And she practiced with that partner beforehand, as this is not something one may do spontaneously with a random person and and out out the blue, just because they feel horny and 'dominant'. I am also gonna bet that it was his, not hers idea to fuck this way and record it for posteriority. Dominance is also about initiative.
You probably would clean yourself out first. You might wear a plug, although, it isn't strictly as necessary as you're implying. Usually, foreplay is a thing. And "Eat my ass" is usually a pretty dominant request in that category. Now, I can't say I've ever been rimmed personally, but playing with yourself, or getting someone to play with you is enough; you don't need to wear the plug unless you're literally planning on hopping straight onto the thing. And even then, you don't really need to wear it for very long. Hell, depending on the plug and dick, putting the plug in and taking it right back out could be enough. And I mean, just clenching and relaxing repeatedly is enough sometimes, but that's for people more experienced. I can do that for a lot of things, but I've been around; I know what's going on down there, and know when I'm ready personally, very well, especially considering that I'm usually taking the exact same things. You need more prep in porn than IRL, for a couple reasons, but to be fair, like you said, they don't normally show the prep in porn. Bigger sizes, retakes, those sorta things are the cause of a lot of the extra prep. It's harder to get something to work and look perfect than just get it to work good enough. In sex, you're just trying to make yourself and your partner/s feel good, in porn, you're trying to get as many people as possible off by seeing it. Sometimes that means shooting a 10 minute scene 5 times. Getting fucked for 50 minutes is gonna need more prep than getting fucked for 10. Well, I've never done porn, so that's me comparing my prep to what I've seen in behind the scenes vids and interviews so that part might be a bit inaccurate. Oh, and depending on where you are, if you're filming it and everything isn't sqeaky clean, if there's even a speck of brown (that isn't skin) it's illegal. If you're at home it might ruin the mood, but won't potentially get you fined. All of that being said though, over-prep is definitely better than under-prep if you aren't sure. But if you aren't sure, you probably aren't a dom anyway.
On the other hand, a dominant anal penetrator does not need to prepare themselves for the act. They just need to convince and respect the boundaries of the bottom to adjust the pace and intensity of the penetration accordingly. Lube? If you haven't got any, just tell the bottom to suck the dick and cover it copiously with saliva.
If you think Dominance in real life is about spontaneity, you're the one who's stuck in a porn fantasy. If you go up to a random person and tell them to suck your dick so you can put it in their ass, they don't do it, you get arrested. There's dozens of conversations that happen in real relationships before that. You covered that a bit about respecting the bottom's boundaries as a top, but you're greatly understating how much work it is. It's just as much prep either way, top or bottom. Especially considering that unless you're into scat, you need to prepare the bottom even as the top. In the words of a comedian quoting his friend "I'm not trying to get cheese on my dick". But if you want to allow the top to be into that shit, the bottom can be too, so the bottom doesn't need an enema if the top doesn't need the bottom to have an enema. It definitely isn't my thing, but hey, to each their own. The bottom has to have a bit of experience, but so does the top. If you've never masturbated or had sex, you have no chance of dominating someone sexually, even if you're putting your tab A into their slot B. The Bottom needs a bit of foreplay, or to wear a plug. So does the top. If you aren't hard, if the blood isn't flowing to the right area in the right way, you aren't penetrating someone. That's why Viagra exists. And the bottom doesn't need to run and get a prescription, then go to a pharmacy to clean themselves out. I mean, you can get that shit delivered too even without a prescription depending on the brand and where you live, but that's still a fair bit of prep work/time. The top can tell the bottom to suck their dick with no lube. And the bottom can tell the top to eat their ass. I brought it up as a warmup, but licking something tends to get it wet as well. All of that's ignoring that prep time is definitely separate from dominance. You prep first, and then play, always. You don't just pull shit willy-nilly. Some people spend a fuckin hour squeezing into very specific getups and getting into character, and they're just as dominant as people who don't.