And asking about basic math on download speed is golden. No idea how someone can “manage a team trained in classic web design” without that knowledge and then pretend to care about performance.
Libraries like dayjs add complexity to the overall codebase and it's another piece of code you need to keep track of, update, and repair when its makers decide to go a different direction with it or some script kiddie decides to introduce a backdoor into it.
I think your larger concern shouldn't be about the "clueless people" who are commenting on this thread and rather the number of upvotes my comment got (especially compared to your rant). Clearly it struck a chord.
People are commenting and upvoting because the choices that went into building React leaves a lot of room for frameworks like Nue, Vue, hell even HTMX. Just because (it sounds like) you've staked your career on thinking React, the McDonalds of frameworks, is awesome doesn't change that.
(Another tip: Don’t bring votes into discussions, it’s both against site guidelines and laughable.)