Let's consider something like Notion or Slack. It's sort of document-based but not entirely -- you can mention other users and other channels names. Some users have access to some channels and not others. And in Notion's case, users may have unique access to 1000s of different documents.

It seems like your solution requires essentially sharding your data based on permission which can get pretty complicated for many collaboration-based apps with lots of shared content and granular permission controls.