That's a way argument though; just because these are metrics on which frameworks are compared does not mean that there is no comparison possible. In fact, I'd say quite the opposite!

And the analogy falls apart when you consider that modern web frameworks are invariably slower or roughly equal in performance to its vanilla JS counterpart, but never faster

What are you measuring? I'll bet that React will be a whole bunch faster than whatever DOM reconciliation library you build up from scraps of vanilla JS, in the process creating your own half-implemented framework (because I'm pretty confident that nobody builds an entire application using copy-and-pasted Javascript.)

In the car analogy the improved performance of modern cars have more to do with mechanical engineering than software

So what? It's irrelevant. Mechanical engineering of a modern car is also much more complex.