Dark and Light P2W Eidolons work a little differently.
They're 80% base, and only 100% if you're running 5 support Eidolons of the same element. Such as Medusa for the Dark one, for example. That gives some value to the worse off Dark Eidolons but...
It's not like you'll ever find a P2W Eidolon without rolling into one, so eh?