are you seriously saying you want to have clear "power rankings" in a series? Kind of like the insane amounts of time the guys at the WoT board put into the One Power rankings? It's not like that sort of thing exists in the real world, either.

That said, you're right that this seems like a rather strong disparity, but it makes more sense if you consider a few subtler factors. Raest didn't become a Tyrant through sheer hand-to-hand combat badassery, and what with him being Jaghut, his magical powers aren't really of the kind you can easily use in combat. There were other factors at work there - and indeed, one gets the impression that humans back in those days didn't have magic as powerful as that which they have at the time of the main plot of the series (nor Moranth munitions, I should add). And as for the Dark Hero Badass, it's actually mentioned elsewhere (but probably a good many books later, in classic Erikson style) that he was still holding back a lot when fighting those three mages.

It's definitely true that the series chooses to have tons of less fleshed-out (and often rather similar) characters instead of a few iconic ones like in GRRM. There's only some that one can care for and identify with - and a good many of those die, so yes, well.