Yeah, I mean it's still a good bit of grinding, but I have >40 crit boost, >20 capacity boost, 23 bow charge+. I played the base game and Iceborne a shit load, but compared to the 2-3 capacity boost and bow charge+ that I got in my entirety of playing world, I think it's safe to say the rates for these are considerably better now even though I don't have the actual numbers to prove it. Other people I have talked to that have done a lot of tempered investigation grinding report the same.
Still the issue remains that if you are the kind of player that moves on after reaching endgame, you probably won't see very many of the rare and powerful decorations. They have a pretty low drop rate from anything that isn't a tempered investigation. Definitely one of the sour spots especially since Iceborne's sets seem to rely heavily on powerful decorations.