Same. I even came across this comment after doing that. Did everything it said (browser.cache.offline.enable perf wasn't there for some reason, so I made one) and still no change. Changed the values of perfs mentioned in my post again as well, combined with that comment's proposed changes but still nothing.
And yeah, it's 1440p but I've tested this on 1080p videos as well. Length of 1440p video is 2-3 mins and the 1080p one is just over 11 mins.
Honestly, I give up at this point. Btw, thank you so much for trying to help.