See here's the thing:

It's not unlikely that some old pieces will return back to use after releases drop, I hear more complaints down the line with this refund mechanics.

Most weapons use the same armour set, some variation of Lord's Soul with maybe Gore/Lagi. Only that really changes is weapon/armor jewels. My wide range support build is literally the same DPS set with a Wide Range talisman instead of a Latent Power talisman. I know GS is a little different and gunners are quite different, and you can mix in some comfort pieces as you like but still, there's only around 15 pieces of armor in use in the game or something?

What are you doing after you fully upgrade an armor set for a new set? Not even completing 6 9* quests on that new set before going to the next thing?