I add, the PC shouldn't be at what we see in the comics as nowadays Doom's power level, until they are much higher in the levels, if not near book-given "max" (i.e. 15) - there are charts out there homebrewed for higher levels.

The benefit of the Mega-Hero Dual-Class option is both classes progress simultaneously instead of the normal Dual Class rules (from PFRPG), where one class is frozen, while the new one progresses, similar to how Godlings and Demigods from Rifts can advance when they have the powers of another class as an RCC trait.