Yeah, that's why they fit more in 76. They were created by pre-War experimentation inspired by real life government experiments and are localized to one area.
It's not watertight but again, it is probably their best excuse of the 3 they've given.
While I largely agree with you, I thought you said the lore is inconsistent so it doesn't matter?
EDIT: Oh, wait. I kinda see what you're saying now. My point is that the all the Super Mutants are, gameplay-wise, are big, tough guys. You can write a big, tough enemy class into your game a million different ways, which they did more creatively in Point Lookout. It wasn't a choice between inconsistent lore and fun, they're just lazy.