Is it really React or the stuff it lets you bring in? Many React apps have at least one big widget set (say MUI or reactstrap or …) and then a number of “best of breede” components that do various things. It’s rare for components to be styled with plain CSS these days so you probably have to bring in Emotion and styled-components and Tailwind and …. It is all code that goes into the bundle and it’s a burden on your mind because these are all leaky abstractions and don’t absolve you of understanding CSS.

If Preact truly was as feature complete as React, it would be used by everyone by now – it's old enough for most teams to be aware of it. The fact that it isn't widely used is case in point.