Most Civ players try to find a level that challenges them the most without resorting to gaming the broken AI and micromanaging every single aspect of their play.
I think this is true.
Emperor is basically the last level where you can do that while still enjoying the majority of the game, and without turning it into a "who can win fastest" contest.
I don't think that is true. I play pretty causally and don't bother locking tiles, but I can win half the time or more at Immortal. I am not good at the whole who can win fastest approach (and don't try) but several board regulars complain that Deity is too easy. So maybe even Deity games can be enjoyed for the majority of the game?