TMG, you are correct that leagues skew results, but it is not true to say that being WTA makes this a bigger deal. GFDT is worse for skewing, because it is near to PPSC and yet games are WTA, but if the leagues were PPSC games, that would have the same effect.
One only has to look at the rarity of a league win to see that it does not, in fact, matter that the "payout" from a WTA win is high.
"Perhaps we need a more extreme definition of WTA such as winner takes all, yes, and for any other result a player gets nothing"
Hence the masters. However, if you used that for rating, nobody would choose to play that system because you'd so rarely get a result.