Incidentally, that's the kind of thing I meant when I asked if this "indeed happens on all Kobos?" As stated in the linked references I was well aware that it was possible on the Kobo Touch, for example.
Edit: I just updated from 4.5 to 4.15 to see if there was anything new in the Linux kernel. There wasn't, at least not in this regard, but I do notice the wording changed from background sync to automatic sync.
Edit 2: also also,
here's an example of a customized Kobo kernel without wacky behavior. Concretely, it sends EV_SYN so the touch events
actually work how they should, it doesn't have a wonky framebuffer, and it supports multitouch because the hardware does.