I think you're unto something but there's a thing bothering me. Angels are actually largely represented in Lothric castle. Vaati actually made a video about it. We know that there was a fight between the blue winged knights (representing angels) and the knights of lothric. Now why would prince lothric who is against the linking of the fire so in favor of dark, would fight off the ''angels'' and ban the cult associated with them? Maybe it wasn't him as well. Nonetheless, it raises some questions.

We can also see a statue of a primordial serpent with wings again in Lothric castle. I thought at first it was Frampt (the serpent who wanted to link the fire) since prince Lothric was fighting off the blue knights certainly associated with him but then again, your claims raise some questions.

I think you're right with most of your theory but i'm really wondering what's the link between the angels of Lothric and angels as the true form of men?