Source of my previous claim in the bottom of the comments on this video: https://youtu.be/RFdD4Sqe7i4
Seems like adding dozens of painted stickers would cause perf issues as well
YeeHawi only ask because i imagine that medals are probably the least resource intensive items in the game when compared to cosmetics because they have no jigglebones, unusual effects, look like quite a simple object (to my non programmer eye) etc and you can't equip more than one at a time though i could be mistaken
I think your intuition is right but it seems like the issue comes from the quantity of models and textures rather than their quality (although I'm sure it's part of the problem too).
I don't think it would be wild to claim that this 15 year old engine does not handle asset loading and rendering at this scale, thankfully the game development industry has made good progress on these subjects in those 15 years (the tech behind the latest Spider Man game is pretty astonishing), up to Valve to keep up ;D