That's very true, there are web apps where "cases where we need to minimize server roundtrips" are the default case. For these situations it makes sense to run a lot of the logic on the client.
However it seems like this has been taken way too far -- I run into a fair share of developers out there who look at basically any proposed web app and say, "Oh yeah, this needs to be a SPA built with React." Why? "Because it's better" and then a rattling off of generic reasons that SPA and doing everything client-side are superior. This is basically the modern version of the Lisp fanboy, they find a good hammer they want to work with more and now everything they see is a nail.
These are often the younger guys who have not yet seen this pattern carry itself out over a generation or two of developers -- if there's any reason why tech ageism is amazingly dumb it's this one imo (have the guy on your team who's graduated past the fanboy stage make your tool, platform and framework choices, you will save far more than the premium that you have to pay him).
