> Time spent not doing our own designs (and instead spent memorizing how to use magical frameworks) is time not spent advancing our technical understanding.

I can't upvote this enough. I used to do mathematics, and there was the story of a professor would would hold up a book and say, "You should know everything in this book. But don't read it!" Which is to say, you have to go through the process of discovering mathematics to really understand it (maybe with a bit of guidance when you get really stuck). The skill of building complex software systems is no different.