[streptomycin]

The original plan from Google for the file system access API was to allow read/write of real files, but both Mozilla and Apple said that was too dangerous, and the OPFS was created as a compromise.

Yeah, it's going to be confusing for users when they want to actually want to use one of these files outside of the application that created it. But it's better than nothing!

[justsomeuser]

This does seem strange, as you can read and write whole files to/from the user's file system once they give your app permission.

Adding those API's to read/write parts of the file is the next logical step. But it looks like it is limited to the isolated OPFS only.