Note: even with these great lessons, I still think that teachers will be useful. The lessons could be pretty good, so I'm not sure if they'd be necessary, but I suspect that they'd still be useful.

It seems you're thinking of a system where teachers help students learn, and the students want to learn and apply some minimal effort towards doing so. And where really good lecture material is prerecorded and teachers don't have to spend the majority of their time reading from standardized lecture notes.

But the biggest problems in modern education seem to lie in mandatory grade school, not in elective college degrees. Many students strongly don't want to study (at least certain subjects); others simply don't care enough to put in a lot of effort. The task of the teacher in practice is often to force students to study (or encourage them, if possible). For those students who do want to study, being forced to sit in the same class as those who don't is often a problem in itself.