With the exception of voice chat (which is a seperate issue I've mentioned before), the -only- difference between a good 4 man premade or 4 good pugs is a premade was grouped before the match.
Except, a premade gets to guarantee they get those 4 good players together in every game they play.
A PUG is playing the lottery, and very very likely to get screwed because the average player is not as good as a handpicked team of geared players with the right composition.
You can either continue to screw over PUG's, drive them away, and kill PvP (It's already heading that direction, queue times are starting to look like they did before the server merges), or you can put everyone at the same handicap with only solo queues available. And then the test would become how well you can work with what you're given, instead of your ability to make friends with a great group and then faceroll PUG's less geared with worse composition than you.