> ...What I'd love to have is a deposit of files to be shared within a group of people...
Agreed, this is the key need! For sharing individual files, i think there are plenty of decent options - including this fork of FF Send, which by the way i have used and works perfectly fine. But, that whole desire to have a shared "bucket" or as you called it "deposit of files" or something similar, where a group of people can use as an area to constantly and consistently share files - and i would add to have those files be organized in a meaningful way - is still not something that i see executed really well.
For my family, its pretty simple in that have an existing shared area within our Onedrive, and manage files there...but there are at least 2 problems with that: 1) there isn't an embedded chat/communication mechanism...so files are separated from context of activity; and 2) what happens if the group that wants to share the bucket isn't family, or not connected on a single service like onedrive?
For simple sharing of files *that are ephemeral/not intended to be preserved nor organized properly* lots of people simply use a chat service. I use a dedicated, persistent room within matrix (yes, that matrix which is used for chat/instant messaging), and use it as my own little pastebin, file transfer/sharing system, etc. But, that approach lacks an organizability/findability of whatever files are loaded into it. So, sharing could be achieved for many participants via chat room, but there won't be a nice, easy way to find files shared from say X weeks ago.
I know that i added chat onto what was mentioned about having an area/deposit of files to share, but i feel having such a bucket in isolation may not be enough...i think some combination of chat or communication AS WELL AS an easy to organize bucket of sharing files is the key...i feel that once that nut has been cracked in a way that provides great UX, then whatever that service will be can have the potential to swallow at least a few existing services like dropbox, onedrive, google drive, etc....or, at least for some non-trivial percentage of users out there.