Bit revisionist to say it never disappeared when there was not a single M3 scene of note between the end of FI and fighting the cat in Elbaf. We’re talking ten years where I can’t recall the trio having any scenes together. There’s Luffy/Zoro, Zoro/Sanji, Luffy/Sanji, but no Luffy/Zoro/Sanji ones.
There’s literally more Luffy/Zoro/Law and Luffy/Sanji/Jinbei moments in that time.
To look at it from a non M3 perspective, if Oda reverses course and starts treating Usopp well again, it doesn’t erase the currently ever-extending gap between Dressrosa and the current day where he has been treated as an afterthought. You can’t then post panels from Dressrosa, panels from Elbaf and say “see, cool Usopp never went anywhere” while ignoring the multiple year gap between the two where he very much did vanish.