Except for the fact that most people use these services in the browser even when there are native clients available? In nearly all of the listed cases the bottleneck is almost always the network and not the JS runtime.

Clearly the users are wrong, I guess? Perhaps you should explain to them why your delicate design sensibilities dictate that they should download native clients because you think HTTP has gone off spec.

Let me guess... you're a COBOL dev and think computers should have never developer GUIs.