Agree totally, I think all I'm saying is I don't want a situation where the design team (inadvertently or otherwise) decides the Javascript framework. In an ideal world they wouldn't care.
That's why they'd work in collaboration with the engineers. To enshrine engineering specific things - names of reusable complements, etc - into the design system. The designers aren't deciding on those, but they can still be included to make the most effective and useful design system possible.