Itachi can trigger many times each round and to any kind of attack, including chase, so of course its rate would be low
Tobi on the other hand can only trigger once each round against mystery, so no surprise if its rate is high
Itachi is a supporting ninja. His mystery give you the chance to bombard all other mysteries in round 2 to create an advantage.
Tobi is a attacking ninja so his damage should be high. His revive is annoying but at least you can start a combo on him with normal attack and kill him fast. if you find Tobi to be annoying, then you rage quit with upcoming immune-to-combo-jutsu ninjas