> Turning off all caching layers and opting in where really needed is a good starting strategy.

An even better strategy might be to gather some evidence up front to learn what actually causes the slowdowns before you start implementing something.

> A server-rendered page from a modern framework is fast.

Seems like a massive generalization. The server-side rendering might be fast, but that is just the HTTP layer. What about the lower layers? From where does it pull its data? How well-written is that query? What about the OS, even the VM or physical hardware. Any non-trivial app is going to have far more concerns about those lower layers than the HTTP process when digging into performance problems.

Introverted title. A PWA will want to cache aggressively on the browser so it works offline.