So, every stat is useful in someway, except attack for non-attack champions. Yet, due to gear reasons, we inevitably have some attack on non-attack champions :<

For example, HP is useful in dungeons and Def is useful in CB, and boss are still useful in arena even for attack champions. ACC, RES, CRIT dmg are also useful for all champions.

Attack however is completely useless to Defence and HP champions. I don't know how it can be, but even if it can help in a small way would be nice.

For example attack can contribute to %Def ignore. 1000 attack = 5% or something very small.