There's something to this. The 200-400MHz era was roughly where hardware capability and software ambition were in balance — the OS did what you asked, no more.
What killed that balance wasn't raw speed, it was cheap RAM. Once you could throw gigabytes at a problem, the incentive to write tight code disappeared. Electron exists because memory is effectively free. An alternate timeline where CPUs got efficient but RAM stayed expensive would be fascinating — you'd probably see something like Plan 9's philosophy win out, with tiny focused processes communicating over clean interfaces instead of monolithic apps loading entire browser engines to show a chat window.
The irony is that embedded and mobile development partially lives in that world. The best iOS and Android apps feel exactly like your description — refined, responsive, deliberate. The constraint forces good design.