While I enjoy 3blue1brown's videos they definitely fall under the umbrella of current gen "edutainment" where the goal is to make you feel like you've learned something without have anything really click.
Pretty much everyone I know who claims that 3blue1brown's video helped them understand a topic... doesn't really understand that topic at all.
3blue1brown's video can be fun for topics you already know, providing a bit of new perspective, but I sometimes wonder whether giving people the feeling of understanding without the actual understanding does more harm than good in the long run.
I can't speak generally about all of 3blue1brown's content, but the essence of linear algebra made concepts like eigenvectors and values and what they are click for me, there is no question.
I agree with the GP that you really need to work through a lot of problems to fully understand a mathematical subject. But there are a couple cases where I did have real, lasting moments of insight, and the 3B1B linear algebra series was one of them. Hearing it stated directly that the columns of a transformation matrix are the coordinates of the basis vectors after the transformation (a fact that I had somehow missed across multiple linear algebra classes) turned on a light bulb in my head.
The Borsuk-Ulam theorem is another example of something that seems obvious in hindsight but that I had never run across before.
For me it certainly helped, but only as "additional course material". When I was studying for the LinAlg exam I used the script of my professor and tried to understand chapter by chapter.
Afterwards I watched those videos to "check" if I had really understood.
Pretty much everyone I know who claims that 3blue1brown's video helped them understand a topic... doesn't really understand that topic at all.
3blue1brown's video can be fun for topics you already know, providing a bit of new perspective, but I sometimes wonder whether giving people the feeling of understanding without the actual understanding does more harm than good in the long run.