[jakubmazanec]

React isn't slow. It can be pretty fast (thanks to hooks like useTransition or useOptimistic, and now React Compiler, etc.) - it's just that it takes a lot of learning and work to use React correctly. Some people don't like that, and that's why other frameworks with different trade-offs exist.

The other thing is that React is too big in terms of kBs of JavaScript you have to download and then parse (and often, thanks to great React ecosystem, you use many other libraries). But that's just another trade-off: it's the price you pay for great backwards compatibility (e.g. you can still use React Class components, you don't have to use hooks, etc.).

[simjnd]

I want to preface this by saying I have nothing against React, I have used it professionally for a couple years and it's fine and perfectly good enough.

That being said React is slow. That is why you need useTransition, which is essentially manual scheduling (letting React know some state update isn't very important so it can prioritise other things) which you don't need to do in other frameworks.

useOptimistic does not improve performance, but perceived performance. It lets you show a placeholder of a value while waiting for the real computation to happen. Which is good, you want to improve perceived performance and make interactions feel instant. But it technically does not improve React's performance.