Scaramanga
Brickhead
On the contrary, very good for gameplay, adds more variety. The main reason the late game is boring, is that no Civ feels 'special' by then as 95% of unique stuff has been used already. Sure, later UA/UU/UB should be more powerful than early ones, but so what?
Makes for an interesting "come back from behind" game.
I think I follow you on that gameplay model - I especially like the idea of an American carrier UU - but I think people have shorter attention spans so they need something to bite their teeth into right away, whether it be unit-, building-, or ability-related.