It's still present. JSON/JS parsing still has a delay. And in either case (as the author states) not everyone is using an iPhone over 5G. Heavy React apps are a miserable experience on low end Android phones, even when the connection is fast. I've seen JS/JSON parsing times in the multiple seconds.

There's 5 bars 5G and there's one bar 5G anyway... Citing connection types really is completely beside the point.

My old iPhone handles well react apps, but frequently freeze/crash on heavy advertised pages and pages with huge images/auto loading videos.