Sure, but the way it works any PC can choose any one book, so if they choose the book with the PRCs, and I don't like PRCs, I can't do anything about it. And if more and more future adventures use PRCs (as I suspect they will) it will become more and more common, and likely the adventures themselves will use PRCs in them, and then I have to decide to I even want to continue DMing AL or do I have to suck it up and be forced to use this "option" I don't like?
Well, right now zero books have Prestige Classes. And even if the next one has them, that's still a year at least a couple storyline adventures away. SCAG doesn't match up with Rage of Demons and a simmilar book would be accommodated with the following adventure. Even then there might not be room to fit the RP pre-reqs into every adventure, or only one Expeditions adventure per PrC making those desirable to play.
Your concern also assumed the Prestige Classes aren't good. That's still a big IF. Huge. PrC were problematic in 3e, but so was multiuclassing, new classes, new feats, monster templates, etc. But there's a good decade plus of feedback, which can used to make PrC better than 3e. The concept of a mini-class with custom mechanics representing specialized training or membership in an organization is perfectly fine design.
It's basically a subclass not associated with an individual class so any character can take it. I can imagine one for each of the five factions.
Even IF 5e embraces PrC there likely won't be the wealth of them that we saw in 5e, if only because there's fewer opportunities.
Except all the examples I gave involve having no choice. That's my entire point. I have no choice with AL, or with round-robin DMing, or with having to change material added in Adventures or future splats (and also the opportunity cost of them not publishing something with those pages I do like), or with dealing with the unintended consequences of an option that looked good for my campaign but turned out to not be good for it. The more options WOTC publishes, the greater the cumulative harm to those who don't like those options. So the claim that "Don't like an option, then simply don't use it, it has no impact to you" remains false. It absolutely impacts people who don't like those options, in all the ways I just spelled out.
Do you DM in Adventurer's League often? Or is this just a theoretical problem?
AL is odd, but the lack of flexibility and control is inherent to Organised Play. You don't write the adventures or pick the setting. You don't choose what accessories are used, who you play with, or often even the date you play.
Ditto round robin gaming. You don't get to choose how many magic items are awarded, the setting, events, etc.
Both require surrendering some control by their very nature. If that's the game you
decided to play you have to be somewhat accepting of not being completely in control. And that's where the choice comes in, when you opt to play that kind of game and not a different game (or no game at all). There's always a choice.
Now maybe it's worth it. Maybe an option is so helpful, for so many people, that it's worth them creating it anyway. I just don't like the claim that new options don't harm those who don't like them because they can just choose to not use them. It's not a good argument - new options have negative consequences for those who don't like them in a variety of ways.
I agree. But the alternative is zero new options. I don't think that's a great alternative.
I'm happy with the slow rate of release. And it certainly feels easier to say "no" or allow different options in 5e than in the last couple editions.