> For example, I have to use a third-party library called react-hook-form to build forms

Why? I've written a lot of React and I've never used this library. In fact, I rarely use any React-focused dependencies except a router, as you say every dependency has a cost especially on the client.

React works just fine without dependencies.

Although you don’t necessarily need the hook, writing a large form with reasonable performance in React can be tricky, so I can understand why you would go with a hook for that case.