> the code errored or something else went wrong. You need to refresh the whole page if something goes wrong, which results in having to load a ton of JS every again, negating all possible savings in time and data usage.

Not to mention that some SPA doesn't maintain state, and all the sudden one need to jump through the the process all over again. Personally SPA seems to try reimplement a lot of browser feature all over again in client side JS.