What about a very simple Winner/Looser-Bracket?
My team wins - the next fight is against a group that also won their last fight (and vice versa).
That would at least increase the chance for average groups to be matches against equal groups.
It could simply try to find equal win/loss rate for 1 min and then open to all. Most of the time this would still lead to open matchmaking, but those nice skill/lineup balanced fights every now and then would be a great morale boost for pugs or underpowered comps.
Also I think the 2h timer for same group match up is too high with ~15 grps running in the 8v8 arena.
I agree, i think no timer is needed here at all. Especially if the win/loss ratio is close it might be great to find a group again, where both sides can win.