I agree it's very hard to get premades together, but it may get much easier when other premades aren't preoccupied with pub stomps.
I would not say that premades are preoccupied with pub stomps. Most premades I know host games and then just play whoever shows up - which happens to be pugs. This is a side effect of the fact that it is very difficult to get a premade v. premade game going. There are several features that could make premade v. premade games easier. For example, permitting one person to join the entire team to a lobby, invites to the lobby from the lobby interface, being able to flip between a pw game and a non-pw game from the lobby, and then the holy grail - matchmaking.
Logically I know that win rate and team % is needed. My guess, however, is that premades are basically done after this unless you want to spend long times in the lobby waiting for a game. Basically, this is how I see it. If you are a premade, even if you are only 2 of the 5 people on your team, you will get kicked (assuming you have a decent win rate). That leaves only premade games. Now if you are a 2 man premade with a 60% win rate, do you want to play a premade game with a random against a 3 man premade with an 80% win rate? Chances are no. Any premade with an 80%+ win rate should not even bother to log on.