"HTTP is being used as a file access, state interchange and authentication transport system"

Ideally we would split them out into a dedicated file access, generic state pipe (ie websockets) and some sort of well documented, easy to understand, implement and secure authentication mechanism (how hard can that be!?)

but to you point. HTTP was always mean to be stateless. You issue a GET request to find an object at a URI. That object was envisaged to be a file. (at least in HTTP 1.0 days) Only with the rise of CGI-bin in the middle 90s did that meaningfully change.

However I'm willing to bet that most of the traffic over HTTP is still files. Hence the assertion.

HTTP is just a protocol. Stateful or stateless is orthogonal. HTTP is both and neither.

Also, HTTP has no concept of files (in general), only resources. Files can be resources! Resources are not files.