Your second point is certainly not universal, some people do a lot of work during college.
If you know what you really want to do before college, sure go for it, but in most cases people have no idea, college is a good place to keep busy and learn about your interests.
I was really talking about the specific work (or practice) that goes into being great at something, not about misspent youth.
Let's take a computer science degree and a ten year path to great (whatever that means). If you just measure by time spent, you're maybe coming out of college 5-20% of the way down the path.
But I'd argue that the computer science degree isn't specific enough to count nearly that much. Really, you're graduating as an broadly experienced non-expert who then has to put a boat load of time into developing a specific expertise.
The value of that time spent outside of college completely trumps the value of the time spent in college, even if the amount of time spent is equivalent.
If you know what you really want to do before college, sure go for it, but in most cases people have no idea, college is a good place to keep busy and learn about your interests.