"Empire building" is a crime that I imagine most Emperors have committed, with all its attributions. These atrocities seem mundane, and while not excusable and likely enough to 'get him damned' (at least in a judeo-christian sense), I see it as a far cry from the kind of meta-evil that seems to be suggested above.
Truly awful, sure. Its hard to ignore genocide. The forceful conquest of the Three Seas is not a 'good' thing either. Kamikaze messengers, also bad.
... But he's not a Ciphrang, or a God, who have been ceaselessly torturing souls since the dawn of time. He's not as bad as the nonmen either, who committed atrocities for so long and on such a scale that they created topoi, tore asunder the very fabric of reality with their malice. If you want soul raping meta-evil, there are examples to be found, but not in Kellhus.
Caveat, this is up through WLW. The end is a mystery. If it turns out the Great Ordeal is just some vehicle for his own ends, then he sacrificed an entire nation with no regard for them at all, and this would put him pretty high up on the atrocity meter.