The most powerful warrior.

No, I mean that the basic units are much weaker than the summoned ones.

They are indeed weaker than the summoned ones, but all the creatures in a hero's army at level 20 are much stronger than neutral creatures! And one Phoenix costs 10,000 gold! Check the user manual. I think it can defeat any creature one-on-one! Very high initiative and speed, plus resurrection! That's how it is! Phoenix rules! :)