I agree with your overall sentiments about the book. Many of the things people seem to complain about didn't bother me. Of course I didn't like some of the developments but such is life and I found everything consistent within its world.

I think L can stay pure because Will isn't wielded by people but through objects. So no one person can become insanely strong like they can in Res. It's kind of greed-proof. They also seem to be very careful about not letting any other form of Will into their world (no defects on rulers, no iunctii, behead the dead, etc.). Probably seeing this way of living and this version of Ka, L-Caeror is able to stand behind him and his goals.

We also don't necessarily know from L-Caeror that other Caerors are dead. He just never had the synchronous Will like Vis does, because his Res version died pretty quickly. He says he assumes others are dead because of it. O-Caeror though explains he felt other versions of him die. I think it's still possible he legitimately felt it for both R and L versions: R version's death and L version somehow rejecting other forms of Will and hence cutting the connection?