"Instant" can mean different things to different people.

I have an HTMX/Flask/Bootstrap app that feels instant for most requests on the LAN, except when it doesn't.

Often React apps are pretty snappy, but if you want to do complex data validation on controlled forms, where the state updates for every keystroke, it can drag you down. There are good frameworks for doing uncontrolled forms in a disciplined way

https://react-hook-form.com/

but it's another thing to add to your bundle. React is also not fast enough to do animations so you have a lot of .show/.hide (or display: none) CSS has facilities to do transitions and animations that are pretty good but I always find it a little nervewracking for a JS application to have state in React state variables and any other kind of state. Some ImGUI frameworks have components that look superficially like React components but are fast enough to animate every frame, which makes me feel like I am in control and get the animation to look exactly what I want.

> I always find it a little nervewracking for a JS application to have state in React state variables and any other kind of state. Some ImGUI frameworks have components that look superficially like React components but are fast enough to animate every frame, which makes me feel like I am in control and get the animation to look exactly what I want

I know what you mean there. I had the same feeling back when I was doing frontend things.