I think JS is fine for some UI sugar, but the app should be usable even with JS off. What you are talking about is indeed better accomplished with an SPA.
While "it must be usable with JS off" was true decades ago for accessability and compatibility reasons, this isn't the case anymore.
In my case, the reason for changing and not creating the DOM with JS is pure simplicity. I'll just as gladly make something that won't work, because it cannot be changed this way. Because everyone except for a very few "mormons of the internet" have JS. Modern JS even.
