“then spend zero brainpower on systems without graphics acceleration”

I don't know what graphics acceleration mean in this context, but my 5-year old computer, with 4 Gb of RAM and no discreet graphics card didn't witness any lag.

I don't think it's performance bottlenecking so much as that the site is capturing the cursor and taking over its physics/acceleration, I think? Which probably isn't noticeable as long as the acceleration is similar to how your OS shell is configured, but was definitely noticeable for me on GNOME.