I don't think, one or two transfer windows will solve this "issue". I think, the main thing is, that managers who train, like, love their squads/players will get disadvantage of keeping the players. And that's the biggest issue... no real club will sell his (best) players, only for showing a weakness... -.-
I think, one of the best ideas is, match them on their levels: 1-3, 4-6, 7-9,... so there's every third season the best chance to win the cup.

I'm one of those manager, who builds up his squad over a whole season, where I don't cared much on standings. And now I'm the dumb, because I have a pretty good team for my managerlevel... and that's really frustrating and annoying.