Comic Spoilers: >! Mark’s little brother, who’s established to be weaker than Mark, was able to rip the Maulers apart like wet tissue paper when he was still a child!<

So Mark definitely could have taken the Maulers if he wasn’t holding back.

But, Viltrumite biology gets stronger as you they age, so eventually, those other unique factors just slowly vanish, until you look like you were always a pure Viltrumite.

!Aren’t the Thraxa/Viltrumite hybrids way weaker than Mark or other full blooded Viltrumites? They’re pretty much cannon fodder at the end!<

True, Invincible goes so far beyond just being a story about Superman if he were a dick.