so if there isn't even enough time to learn practical but sub-optimal solutions, a dev should instead absorb books about IT, mathematics and programming theory?

great advice...unless any part of your equation includes receiving a paycheck.

Don't make it sound harder than it is. Each of these is 30-40 hours of work for undergraduate students. You don't have to quit your job and join a monastery to study compilers. It's interesting, challenging and fun for those of us into computing; and it pays back the time spent learning.

So now I have a list of things I should learn according to a random person on the internet, that no one in real-life ever gave me before. How am I to know that this list is the one? Why not every similar list that has ever been given to me?

And how am I going to develop the front-end of our new website after learning everything you named? There'll still be a lot left to learn before I can even hope to have produced something.

True.