Device performance has been growing in diversity as we approach smartphone saturation (the last couple of hundred million flipphones getting traded for < $100 low-end smartphones). I'm working on an update to this series, but here's a recap from last year:
As this relates to latency, JS-mediated UI is slower to materialize for a host of reasons, not least of all the problems with getting it across the wire (as you note). Naive SPA designs tend to serialize what should be parallel (data fetching and shell setup). Getting better at this requires more sophistication, whereas teams that stick to basic HTML + light progressive enhancement tend to end up with simpler systems that are faster for light-to-medium session depths and are easier to diagnose/fix when things go sideways.
https://infrequently.org/2021/03/the-performance-inequality-...
As this relates to latency, JS-mediated UI is slower to materialize for a host of reasons, not least of all the problems with getting it across the wire (as you note). Naive SPA designs tend to serialize what should be parallel (data fetching and shell setup). Getting better at this requires more sophistication, whereas teams that stick to basic HTML + light progressive enhancement tend to end up with simpler systems that are faster for light-to-medium session depths and are easier to diagnose/fix when things go sideways.