The big problem with Dynamic Queue

Balanced teams become rarer.

Imagine both teams have a premade trio, now both of them get adjusted mmr to make up for it. But one of them are try hards that use skype and have a plan and coordinated playstyle. The other just met previous game and don't even use skype. Now who is gonna win obviously!?

This same thing applies if you have solos playing vs tryhard premades or casual premades --> in the first example the premades will generally win, in the second the solos will generally win due to the mmr adjustment, i.e. it will rarely be balanced. Less balance means less fun so Dynamic Que will destroy part of the fun through this alone.