Dan LuuHow web bloat impacts users with slow devices:
HazelnootWhile reviews note that you can run PUBG and other 3D games with decent performance on a Tecno Spark 8C, this doesn't mean that the device is fast enough to read posts on modern text-centric social media platforms or modern text-centric web forums. While 40fps is achievable in PUBG, we can easily see less than 0.4fps when scrolling on these sites.If your website is 100x slower than PUBG then you may want to reevaluate what you've done 
Curtis Wilcox@hazelnoot
That quote stood out to me too. I think about why that would be and at least part of it is related to the Knuth quote, the game is heavily using the GPU and parallelization in general while the Discourse JS has a single thread.
Browsers can use some GPU acceleration, including for scroll, maybe there's a problem on this device so it's not being used or Discourse is written in a way that prevents it.
@danluu