Getting the matchmaking right appears to be a near impossible task. Today, for instance, I seeing all 5000+ rune power teams again in all slots and opponents are still shifting between slots.
Roster power is pretty meaningless at this point. Even a few level differences don't matter very much. Everyone knows that rune power is the key factor. Why not just align the matchmaking to rune power of the teams on defense? I'm just making these numbers up, so maybe there are better thresholds, but for example: Easy matches are rune power 3500 or lower. Medium matches are rune power 3501 to 4500. Hard matches are rune power greater than 4500. This would be for level 65 to 70. The thresholds would be lowered for lower level players.
Seems like this would be easy to program and provide some consistency and predictability to the matchmaking.