> It shouldn't be mounted rw

It should be mounted rw because existing userspace expects it to be rw.

> It shouldn't be mounted by default.

It should be mounted by default because it's information that's relevant to various pieces of userspace.

> It shouldn't even be a bloody filesystem.

With hindsight, it should absolutely not have been a filesystem. There's very little metadata associated with EFI variables and the convenience of exposing this in a way that can be handled using read and write is huge, but real-world firmware turns out to be fragile enough that this was a mistake. But, in the absence of a time machine, there's very little I can do to fix that now.