Seems like the CR was a bit low in comparison to APL considering you add Mythic tiers to APL, this encounter was at the same level making it far too easy for a bunch of level 20's with 5 tiers. Without the dimensional dervish tree this fight probably would have lasted a bit longer, maybe drop a character if a lot of attacks were focused on just one character.
Wizard could have used mythic power to add 1d8 to his CL check to beat spell resistance and make himself a fine pair of shoes.