Oh we don't know if they have vessels or not. Maybe they do but there are simply much less of them than there are demons, so we didn't run into any of them. Maybe they just prefer to not make themslefes known and stay hidden.So why Angels don't have vessels like demons? Makes no sense to me.
And those slow-mos don't make sense either.
Might also be possible that they aren't allowed to have vessels by whoever might be their ruler, resulting in them becoming outcasts like Eva should they break that rule.
Dunno, but I never had a problem with those slow-mos, they always kinda made sense to me :/ Imagine it like throwing a stone into water, and how the waves caused by it diffuse. Whenever those waves hit a turning point, a disruption is being caused, creating a Rift, sucking Dante into Limbo and making it seems as if time slowed down.
idk that's how I always explained it to myself ._.