So before I got that first job, I focused on learning general things to raise my ceiling, so I studied text books. OS, DS and Algos, Calculus, DB Implementation, and others.
Now that I have my job, I’ve focused on the areas that i am tasked with in my day job, like DB deep diving and Statistics and Linear Algebra.
I always felt that any side project I would focus on would impose too high an opportunity cost because I fealt I was learning better things.
I am still growing and will continue to grow as long as I’m in this field but my github has nothing noteworthy to show off.
That said, I believe your point is correct in the abstract, namely, that Devs who spend time outside of the office to level up will be better than those that don’t All Other Things Being The Same, I’m just saying that side coding projects isn’t the only instantiation of that activity