Generally speaking a regular dev under normal time/budget constraints will.het better performance out of React or Vue. It takes more time and more expertise to get that "optimal" VanillaJS performance. Analogy: Ruby vs C.

I disagree.

With React, you can quite quickly stumble over performance bottlenecks in non-trivial app when you don't know what you are doing.

Especially on mobile devices.

Could you give some examples? When it comes to trivial apps I'd say jQuery could be fine, but it feels like kind of working against what it was designed for. But for non-trivial apps I can think of at least as many jQuery 'gotchas' as I am aware of in React.

If your app is non-trivial, I expect maintainability nightmares in vanilla long before performance issues (which will be in both for people who don't know what they are doing).