I think if you just want to be a front-end app or web developer than a bootcamp or alternative education can suffice. And I agree you learn more by producing work. Teaching yourself how to use frameworks like bootstrap or angular is easy. But teaching yourself fundamental CS principles like traversing a linked list or rotating a 2D matrix is much harder, and the payoff comes much later.

For example, you mentioned that you do backend dev. Suppose your boss asks you to do load balancing to handle server traffic. You could probably hack something together with AWS tutorials and Stack Overflow, but do you understand the principles behind it? Can you actually improve whatever it is you built? What if you can't afford AWS or you need a custom solution? If you don't know or can't do these things, then you'll never be as valuable or useful than someone who does.