> In many cases, simpler code is faster, and fast code makes for simpler systems. (...)

I wholeheartedly agree with you here. You mentioned a few architectural/backend issues that emerge from bad performance and introduce unnecessary complexity.

But this also happens in UI: Optimistic updates, client side caching, bundling/transpiling, codesplitting etc.

This is what happens when people always answer performance problems with adding stuff than removing stuff.