Yeah, Val and Xel are from the same worldtime. Please do use. :)
I haven't seen all of that, actually; not any of the bits involving Rezo. But, yeah, I'm not on board with that interpretation, either. The first season was pretty clear on Rezo having only come to the dark side late in life, as a last resort, and I'm sticking to explanations for his behavior that gel with that...
Oh, sure, Zel's mental blocks completely make sense. That doesn't make Xel feel any better about him, though. First, because Zel consistently trashes someone he cares about and won't hear any alternative explanations for things that have happened than the ones he's decided on, or even allow that such might have been possible elsewhen.
Secondly, Xel resigned himself to a lot of pain and trauma with the mantra that it was for the sake of his human pack. Zel is the last of that pack, and unlike the Zel from the sub anime, who was suspicious and cynical but was actually not completely unwilling to consider the possibility of being wrong even about important things, this Zel (who I believe is dub-inspired, and is therefore a lot haughtier and more rigid) has not been interacting with Xellos (when there was any of that) in such a way as to help Xel keep feeling that what he went through was worthwhile. Which is especially hard since he's only completely over it physically.
And then there's the other, unrelated issue Xel mentioned, and his fear that Zel is, whether actively or not, poisoning Val's mind against him.