I think that's a main difference. With a degree you tend to learn / get taught things upfront of which you don't know whether you'd ever need them, and you may not. You kind of trust, or hope, that what they teach you has some relevance and is useful.

Many subjects from courses I took during my degree I'd never have picked up "on the side" during my jobs that came after. But I can actually also confidently say that each and every course I took left some impressions/concepts in my head that later became useful in one way or the other. So for each course I took, had I not taken it, I'd be missing something. Of course there is opportunity cost: could I have used that time in some better way, i.e., even more efficiently? Not sure. There is also the question about the courses that I did not take because, well, there is only so much space you can cram courses into within 6 years :) but maybe there are diminishing returns as well, since many things tend to overlap.

I think the most important benefit of a university degree is not so much what specific fundamentals you are trained in, but that you get an idea of what it really means to know the fundamentals of a subject and how to get there. Later in your career, you can then use these strategies to deepen your understanding of everything that comes your way. Of course, it is easier if your education roughly matches what you will find on the job. But you never know what aspects of your training might help you later on. In my case, I would say that the many difficult debates and deep essays in philosophy prepared me much better than probably computer science might when it came to working out a plan for a software module with others and writing an accurate specification.