“Most” react apps needing “seconds” definitely needs some citation or evidence. Even in fairly heavy and laggy react apps, it’s still usually network latency, waterfall requests, ad/tracking bloatware, large asset sizes, and the usual old classics that cause perceptible slowness in my experience.
It's hard to build non-trivial web UI with any technology—React is just what's familiar. If Angular had won (god forbid) we'd be seeing all the same articles written about how bad Angular is.
You probably never see what reddit like after it just get rewrite. https://www.reddit.com/r/bugs/comments/rj0u77/reddit_redesig...
I won't say most react apps performs like this. But it's what you will get if you ship a big react app without optimization at all.
Other framework mostly have a much saner default (for example, component without argument change does not re-render). So it will work well (not best though) even in large scale. But in react they are all opt-in.
In my humble (backender) opinion, if it's hard to use a tool right, that counts as a cons, and that must be accounted for when choosing which tool to use.