User blog comment:IamJakuhoRaikoben/Chapter 379: Tartarus Arc, Part 3: Underworld King, Review./@comment-5598380-20140404081256/@comment-7418318-20140404150153

They are only similar if you just scratch the surface I think, but in depth they are quite different.

Mogamett always wanted to help people. First all of them, then mages as rulers and goi as the ruled and finally completely subjugating or wiping out all the goi. But he was always aware of the relation between mages and goi and intentionally intervened in this relation.

Precht on the other hand was looking for knowledge and power. That non-mages and weak mages would be wiped out was just a side-effect of his quest, rather than something intentional like Mogamett was doing.

But I absolutely agree on Precht not necessarily being redeemed. A world where Humans can't use any magic at all is the absolute opposite of his dream of the Great Magic World. And he might also be pissed about Franmalth absorbing his soul, so his help might be partially motivated by the need for revenge against Tartaros.