There's gotta be a better UI/UX for this. Right now it's a royal pain - the best I can figure out is to take a screenshot of the 4*+ souls that I have, and then split-screen view the stage in the special champ select screen (which has the filters to show only the usable champs).

That's "sorta" okay for me since I've been playing long enough that I recognize "most" champs just by the icon, though even for me there are plenty that I just don't recognize. But man is it ever a pain, and for someone who doesn't know the champs, it's pretty much impossible.

I think the "easiest" solution would be to somehow add filters to the souls/awakening screen, to allow you to apply the same filters that the stage does - though the better solution would probably be to do it the other way around, and offer a way of applying/flagging souls directly from the champ list UI.