[afavour]

> they likely went with something HTML/CSS-based, which would explain the performance issues.

This is the case with a lot of apps that still manage to be performant. So it's quite possible Amazon are writing bad HTML/CSS but that's possible in other languages too.

[nyarlathotep_]

Indeed, YouTube uses some sort of stripped-down Chromium (Cobalt I think it's called) with the client UI authored in HTML (and friends) for all of their clients and it's not deficient in performance compared to others. The Prime client is notoriously janky, even on Apple TVs, IME.