Noone, and I mean noone, has made more new characters in this game than I. It’s almost exclusively all I play in GD.
I feel certain of that to the bottom of my black little soul. I can tell you without a doubt that, if anything, droprates increased - especially if you have the expansions and access to Monster Totems. There has never been a time in GD where it has been easier to have a character geared well by the time they are levels 20-30. And I mean this from a self-found perspective. Needing nothing from a shared stash.
Naturally, RNG plays a hand, but any person experienced in the game, as you claim to be, should have no issue kitting out a fresh toon in fairly respectable gear by that point. You have multiple avenues at your disposal between regular gameplay, trawling the merchants, crafting, and totems - a mix of using all these methods can nearly always consistently guarantee that your character will be sitting Aces high by the time they are 30 and there-on for a good while.
One area I do not have a lot of experience in is co-op play and I believe I see you say that you play with someone else? If so, then I can’t speak on drop rates in that particular scenario. I would say verify your game files if you haven’t already… and then go from there.