If we would start webdev from scratch and had to choose between:
- CSS vs css-in-js
- REST vs GraphQL
- Templates vs JSX
No sane person would choose the first options.
I think it's a fair point that a "new web" would be all written in a single language. However the best bit what we have is you don't need to know CSS, JS & HTML to make a webpage & doing it in whatever works is totally ok.
If someone approached me and said "Here is a new platform, you've got to learn 3 languages to do it" and someone else said "Here is my platform, you just need to learn 1 language", the second would be a much easier sell, especially if I'd never programmed before.