This discussion is a bit like how assembly programmers used to defend not moving to a high level language long after the performance benefits were not worth it any more.
But we're not at that point in the web yet. The performance benefits are worth it. Just try out JQuery Mobile if you want to see what wasted CPU cycles can do.
The point is we're well past the point where grasping for the asm-equivalent from the start should be the default unless you happen to specifically target one of those niches.
That's still going to be a lot of work if the performance issues turn out to be many separate jQuery calls spread all over your code, which is not unlikely.
Such as?
$ isn't just a syntax layer on top of querySelectorAll. When you do $('p'), it first queries the DOM for everything that matches that selector, then it creates new jQuery objects to wrap each of the returned nodes as well as creating a jQuery object to contain them.
If all you're doing is setting the innerHTML of these objects, it's a non-trivial overhead.
[1] https://github.com/jquery/jquery/blob/master/src/manipulatio...