What you say above is impossible,
It is what I have been told by an actual user on this forum. I don't want to name names, particularly when the poster in question clearly has chosen not to participate here. But I assure you it is a specific person. I can DM you the name if you care enough to know it, but I would request that you not invoke it here, again just to respect their space.
I'm pretty sure you've been in the thread when this person has specified just how much they know about their world. They know every continent, every city on those continents, and most (if not all) factions. They know so much information, it's simply impossible for there to be a location in the world they haven't already described in their notes, or so they claim.
Whether or not a race can fit in entirely, as a unique individual, or is a disruption, has nothing to do with the level of detail of the campaign. It has to do with the theme/premise of the campaign setting.
Except the level of detail is
the reason why the "theme/premise" can't fit it.
Because there literally isn't a campaign theme or premise which is so utterly incompatible with turtle-people that it cannot possibly be done. I'm quite happy to be proven wrong if you can give me, say, two themes/premises that are not literally "Just No Turtles", where it would genuinely be utterly incompatible. "Sword and sorcery" ain't gonna cut it, sorry--because "sword and sorcery" is gonna include a bunch of other Weird Stuff, so the forbidding is still completely on the GM, not because "Sword and Sorcery" actually has any problem with turtle-people or whatever. (As if it were any
less problematic to have elves or dwarves!)
Dark Sun is "sword and sorcery" and it accommodates all sorts of things just fine. E.g. the dray, which allowed seamless integration of dragonborn into a classic setting!
And this is equally false. Nobodies fun takes the back seat. You the player have no right to expect it to happen that way. Your fun isn't more important.
But that's precisely what's being said. Player fun inherently, necessarily, takes a back seat to GM fun. If the GM's worldbuilding fun is impinged upon, to even the slightest degree, it is an unacceptable destruction--so the player's fun
must be impinged upon to protect every single part of the GM's worldbuilding fun. If sacrifices must occur,
only the player(s) must make those sacrifices.
That's not what I would call leadership. In fact, I would call it behavior blatantly unbecoming of anyone GMing or wanting to GM.
Again, I don't expect leaders to simply
suffer all the time etc., they deserve to be happy too. But if
someone has to make a sacrifice for the good of the group? I expect the GM to take the lead on doing that. I encourage the players--including myself!--to take one for the team now and then too, as that's one way of showing respect for their GM's leadership.