As for why the mouse is fast in Windows the interrupts are handled by the kernel in a very special way to perform almost mind reading levels of speed even over the bloated USB stack.
I suspect it to be a nightmare to maintain as USB upgrades happen but who knows.
I used Windows 7 until my SSD corrupted pretty much 5 years on the day after I installed it on the 400GB Intel drive. It started with games crashing and then after one such crash (black screen, not blue screen) it just refused to boot because some important file was unreadable.
Choosing your SSD will be the most important choice you make in the future, as I said previously I have 2x Windows 7 and 2x linux machines on older drives that have lasted 10+ years 24/7. So something is wrong with modern SSDs, no doubt about it.
About sites deprecating browsers, you might be more lucky with really old browsers now a days. My bank refused to work on a 3 months old Firefox, but a 6 year old Firefox (installed to run Java Applets which BTW where WAAAAY better than .js + WASM, and no; they where not insecure like all the naysayers pretend) ran fine with some layout glitches.