> More system calls mean more overall OS overhead [than the equivalent operations performed with io_uring]

Again, this just isn't true. The same "stat" operations are being performed one way or another.

> Also, more fs-related system calls mean less available kernel threads to process these system calls.

Generally speaking sync system calls are processed in the context of the calling (user) thread. They don't consume kernel threads generally. In fact the opposite is true here -- io_uring requests are serviced by an internal kernel thread pool, so to the extent this matters, io_uring requests consume more kernel threads.