D&D 5E (2014) DC in DnD: Superman

[Morrus]

I'm curious as to this ability:

"Physical Invulnerability: Superman takes no damage from any effect unless it is generated by a spell or magic item."

Since virtually every character past level 5 either has magic weapons or other means to inflict magical damage (Monk force punches, artificer infusions, etc.), I don't see this being much of a factor. At AC 16 and 300 HP, he'd get chewed up pretty fast.

A lot of level 20 characters could solo this version of Superman easily.

Given his weakness to magic, a D&D party should be able to. In our world, he's pretty super. In a fantasy magic world, he is not so super.