More so because plenty MMORPGs get away with hybrid jobs genuinely being weaker at each hybrid aspect in return for having two.

But importantly those games (early EQ1, GW2, such stuff) are built around the classes being that way. Pure healers cannot be useful if not enough damage is ever dealt to even engage one pure healer. Naturally the existence of proper hybrid healers who can do healing + X (like current healers being all hybrid healers who do DPS+Healing!) displaces the idea of a pure healer (who spends ~all time on healing) because there is never enough healing need for even two hybrid healers, nevermind a single pure one.

And the same applies to other concepts. We need the battle system to change to meaningfully change combat classes.