React is quite a minimal framework (or not even a framework), actually. It's just that it has a huge following and takes some mind-bending to actually benefit from it.
If your client is an otherwise idle system with the latest browser, a fast wired connection, and the developers carefully monitor time to render.
In most cases, at least one of those is not true and the developers are using something like CRA so your site has a number of users who see tens of seconds of nothing while their Android phone downloads and runs a 1MB JS bundle. Bonus points if the marketing department has tossed in a tag manager which delays that even longer.
> Male gorillas of the Western lowland gorilla (Gorilla gorilla gorilla) subspecies have average weight up to 140 kg (310 pounds) while females have up to 90 kg (200 pounds).