> all the big players have their own deeply integrated solutions

This is exactly why I use Dropbox. I use a single Dropbox account for my family. It's setup with photo sync on our phones so we can automatically share photos together. It's also setup on the printer/scanner so scanned documents are accessible to everyone. We keep documents in it that we can all access when needed. We also access the data through our file browser on our computers.

I feel my use case is simple but it's impossible to do this with the big players due to integration.