True. But a Minotaur can be dealt with and adjusted to the power level of the game.This. Players who don't want the GM to curate a world that interests them within reason really need to go the way of typewriters and VHS tapes.
But, a sentient ooze dual wielding rocket launchers riding a celestial force dragon mount would kind of be out there. But, that is more because of power level and tech level in the world than any attempt at controlling player creativity. But, this is, like you say, subjective. If you are running some kind of Planescape/ Gamma World/ He-Man Eternia cross campaign a sentient rocket launcher ooze hero might have a place. In fact, it would be cool. But a strict Dark Sun, FR, or Eberron deal would break genre. But we are not talking that. We are talking outright banning from games what, for better or worse, are CLASSIC templates that a good player could do well and actually spice up a campaign. I also do not buy the "my world curated" deal. Planar portals and accidents happen. Even if your world had no Drow or Minotaur, think of the epic quest and hooks to figure out what happened or possibly a way back home. Or the RP as a minotauar with the PCs tries to enter a very xenophobic prime world city in that those things are monsters. Some backwater, low magic village on a prime world would not be like Sigil, Union, or even Waterdeep where such sights may be a bit more common.
I think instead of the "my world" stuff, I would be more about turning down a concept due to relative power level. Yes, I am open to letting folks play dragons. But, it is no fun to the other players if everyone else is playing the level 1 apprentice rogue or wizard and one person has an ancient red dragon with class levels!
I also have a sneaking suspicion the whole DM "my world, my rules" thing helped contribute to the decline of pnp RPGs at a lot of public venues when the players just wanted something reasonably cool.
Let's shun the problem primadonna campaign destroying players, not the template.
Hell yeah. I get a good player out of the deal that just happens to want a Minotaur and I can give him what he wants within the power level of the story, I give it to them. Fun> anal settings. Plus, it keeps me on my toes and makes me a better DM. I am NOT a leader or curator or whatever. The players are there to help me create the story. I am merely a MMO server that creates bad guys, keeps things moving, and tries to create a sandbox with cool things and characters to interact with. That way, they come back.