power is not everything when you hit lvl 55
you get 3 summon slots . and all the 3 summons power will be added to your main
but during the battle only 1 summon power will be added in the battle
Aside from that, some ninjas doesnt need a certain stats to be cultivated but people still cultivate it, so that adds up more power but unnecessary ( not useful ) power that doesnt do much for the battle

It all comes down to team strategy and countering