It's fairly insane that after seven years nothing has changed. I don't keep files in the cloud because they may contain data I don't want to risk losing custody of. I recently had this issue crop up because my iPad made it a painful ordeal for me to download a file, add a comment, have a colleague edit it, get it back, put it back on the server, due to the fact that none of the apps are allowed to access any common storage.
Specifics; I'm working on a php file on a web server and I want to send it to a colleague for edits after adding a comment to my code. Only way to do this on my iPad is download the file from web server in one app, copy it to Files (two copies on iPad now). "Share" the copied file to my html code editing app (three copies on iPad now). Make my changes, send it back to Files. "Share" the file again to Outlook so I can send it. File is edited and comes back, save back to Files, Share it over to transfer app, upload back to server. Not having apps able to access a shared storage area probably wasted two minutes of my time, for one single instance. This is a productivity killer and makes the platform useless to developers.
Want an even simpler example? If I compose an email in Outlook on iOS, then realize I want to send an attachment with the email, well I can't. I have to stupidly send it separately since Outlook can't read the local storage, or, select all, copy, save draft, exit, go to Files, 'share' the file I want to attach via Outlook so new message starts, paste my text back in, send, delete draft I was keeping for safety. So dumb...