I'd say it's the opposite. These no-jQuery methods are good if you are "just trying to tack on a dropdown menu onto a decade old Wordpress theme", however if you want to manipulate DOM in a more complex manner and do not wish to pull in an entire frontend rendering library, then jQuery is perfectly fine.

You will have/want to factorise these methods anyways because some of them are just ridiculously long. jQuery has already done that and at least it is very consistent.