"One day I want to make a blog league table in which people suggest artist / musician names in pairs and I select a winner, then the winners fight the winners, until we get an ultimate winner: the greatest artist (according to Momus) in the world!"

I wholeheartedly endorse this sort of contest. It'd be like geeky music adolescence all over again: endlessly amusing.

Wouldn't there have to be some kind of initial grouping of musicians/artists into conferences or something, based on a certain degree of similarity? Thus Bowie would perhaps be in a conference/league with, say, Roxy Music, since (perhaps) neither of them could be, at least initially, in the same league as, I don't know, Black Sabbath.

No, I think anyone could be with anyone. You know, Ivor Cutler / Pablo Picasso. (That would be a hard one, actually.)