It all depends what you want to build. If you build a simple website, sure go with plain html/css/js. However, if you build something that needs let's say performant DOM updates, React or similar will give you that for free, and otherwise you'd have to develop and test it yourself.
I have been programming long before LLMs, and it was painfully slow, but the lessons stayed with me for a long time, and after some time I was able to spot architectural problems before they became problems, because I suffered many times before.
When I'm building with AI now, it's much faster, yeah, but it's extremely difficult to learn these patterns, so I feel like slowing down the pace when working with LLMs (although very difficult), and researching things properly will allow you to develop these muscles, and bring benefits in the long run.