If CSS is Turing complete, that means it has a virtual machine with parsing and so forth. That means that difference between it and JavaScript is just syntax. (Same for any Turing complete language)
Not just. There’s also the issue of complexity. And JS is considerably more complex. Just think of all the APIs that are immediately available at runtime in JS, for one. It takes up far more memory and CPU cycles to initialize, the language itself is much more complex…
I am not quite sure I understand what you are getting at. Surely, we don't have to go into why syntax is extremely significant for feasibility of implementing features. I mean, we don't code in assembly much these days, do we?