Without the helpful abstraction of files and folders, all we'd have are bytes stored at various addresses or sectors of the hardware.
I agree with most everything else you said, but would slightly push back on that. I actually quite like the idea of non-hierarchical blob storage searchable via arbitrary indexed metadata, as well as the idea of content-addressable storage (e.g. with magnet links). While folders are an elegant abstraction, I really feel that we shouldn't be beholden to it.
Without an OS, you've got a CPU and memory-mapped hardware devices. You certainly don't have files.
On that note, I remember how absolutely ecstatic I was when I first set up Sublime Text and discovered that unsaved editor tabs always reliably survive restarts; it essentially flips the script, whereby I've lost multiple saved files by accidentally deleting them, but I've never accidentally lost work in unsaved tabs, and I've never actually had any interest in figuring out where and how these tabs get persisted - it just works.
It's a hard question to figure out what's the proper level of abstraction for this is. And while I strongly resisted it originally, I am becoming more open to the argument that many people don't need to "know" what a file is, to benefit from their computers - that as long as they can "save" their work, and "send" it from one app to another, they'd be able to get all the productivity that they are looking for.