I’m not debating the importance and whether or not someone is required to or should use these during their projects, use whatever tools you want to aid you, but only when you understand what each of them does. It’s never good to be completely dependent on them because there will be a time where a different framework or pure JS or CSS is needed. Learn how to do a basic grid layout with HTML and CSS, learn how to manipulate the DOM without resorting to jQuery.
Will it be slower sometimes? Heck yeah. jQuery makes some things so much simpler. Sure a lot of basic jQuery can easily be replicated with pure JS but as you get more advanced, there’s more to understand. Instead of breaking out Bootstrap, take your time to learn what it’s actually doing. You’ll only benefit in the future. Like I said, not all projects will require you to use them, sometimes using them would be counterproductive. Therefore, do yourself a favor and learn to crawl before you run.