I use syncthing to sync files from several folders of my phone (internal app storage) to folders on my laptop (usually as a backup) and viceversa (usually because it's easier to download some files on my laptop, think about GPX tracks). This means that I need synchthing to access all those folders.

I also use an open source file manager app to access files on both internal and external storage. I need it to access all of it.

I understand I'm not the typical Google user as I'm logged in only in Google Play and Google Drive, which I use for work and not for backing up stuff. However if they turn Android into iOS maybe I could finally buy an iPhone SE when the last small factor Android phone dies. Not really, because that would leave me with a much more closed down environment. Alternatives? Maybe a Linux phone if there will be something around, but I'll have to keep using an Android anyway, so going around with two phones, which is worse.

What Google should do is give an option to lift all walls between applications (or root the phone). Void warranty and the likes, it's fine for me. I'm replacing all closed source apps from untrusted parties with open source ones anyway.