Super rare=strongest in the banner(treasure).

The only thing that makes a ninja overpowered is if you don't have a lineup to contain them. Roshi's biggest weakness is pure ninjitsu as it doesn't make him stronger. Han on the other hand is very manageable if you can take out the back line. The ninjas you get for free over time without dropping a seal scroll have no chance unless you're much stronger than the people you're against. You will need a few banner ninjas like SN, and kage's like mei or KK Garra to deal with them. Avoid auto heavy teams. With any jinchuuriki lineup you'll want to run someone who can debuff like Gaikido as well. I think they're balanced for the most part. Ive yet to get 100-0 stomped by anyone even against people 10k higher.