That’s one of the best cases of a decent monster that gains a lot support wise for evolving him. Imo there a quite a few more monster should be like him, where there’s a very clear reason to evolve him, but you can still use him with much less potential
They gave him both the passives in the second form, that’s why. If a monster has the final form passives in all their glory then it makes sense it only has two active skills.