If I proposed the suggested game and a player said they wanted to play the last mage, I’d not assume “oh, Nick’s being a jerk”… I’d assume “Nick seems to have a strong idea based on the premise of the game”. And I’d want to discuss it and examine it.
I'd assume Nick is for whatever reason refusing the thus-far-only stated premise of the game, even if he's not being a jerk about it and thinks he's got a good idea.
Because despite your optimistic reading of the situation, Nick's idea is
not based on the premise of the game but is in fact directly opposed to the premise of the game as stated.
Because the player isn’t refusing the premise. The player is challenging it… and doing so through their character concept. That’s an expression that engages directly with the premise and one that comes loaded with conflict.
Challenging the premise like this is synonymous with opposing it, I think. And if all the players thusly challenge the premise, be it in the same or different directions, then either there'll be a lot of disappointed players or there won't be much of that premise left.
Ummm… so be it? What’s the problem?
None, if the last-mage's player is willing to accept that there are now no mages left at all and comes back with a different character concept for the replacement.
IME that would be highly unusual.
No, not really. It was suggested that all the characters be as connected to the central premise as this. That they all be uniquely tied to the setting… and one another… as possible. Most seem to be ignoring that suggestion in an attempt to paint the hypothetical player as problematic.
I can certainly see building a character concept and goals around finding out
why there's no magic (if such a thing can even be explained), or trying to bring magic back (if such can be done); as both of those examples start out by
accepting the premise that there is no magic now. Wanting to play the last mage blows that premise away; even more so if the other players see this mage and say "Hey, I want one too!".
It’s all made up. We can come up with any rationalization for the inconsistencies as we like. Feeling beholden to them, though? That feels like maintaining the status quo simply to do so. What’s the point in that?
Internal consistency. Middle Earth, despite the oddities pointed out in the OP, has a strong underlying internal consistency which goes a logn way toward making it believable enough that we can immerse ourselves in it.
I’d much rather have characters and situation for play that are more rife with conflict.
In-character conflict, sure. But this seems more geared toward player-v-GM table conflict, which rarely if ever ends well.
More unique to the point where this world and the characters are inseparable.
I'm a fan of the Gygaxian notion that characters can be (with the GM's permission and at least a modicum of system compatibility) transferred between worlds/games/campaigns. Tying characters to a specific world plays against this idea.