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.
That's a false logical conclusion.
Preact (and others, like Svelte and Solid) are not only "as feature complete as React", they don't need some of the features of React (hooks are unnecessary when you have proper reactivity) and they are better at certain features (like SSR).
People using or not using them has nothing to do with feature completeness.
E.g. you don't need React hooks because Preact has signals: https://preactjs.com/guide/v10/signals/
Does this mean that Preact doesn't have feature parity? For a very strict definition, no it doesn't. Does it mean you need to sacrifice anything? No.
Same goes for many other frameworks. In modern landscape when it comes to features and abilities React is actually quite a poor offering.