It's funny you mention teachers being bored because perhaps the problem is that teaching is done wrong, it's funny you also mention "maybe you should do an online U, or skip Uni and just read some texts", because that's exactly what I would do if wasn't so risky to trust that someone out there will take a chance hiring me without going through the systematic gatekeeping, with online Us there's an issue of finding reputable ones (at least georgia tech has an online MS program now, might give that a try at some point).
Here's the huge difference between grinding at work and grinding at school, at work you get paid for it, at school you are being made to grind because someone else thinks that's the best way for you to learn, it feels infantile, teachers should only be there to answer and clarify questions, and the material should all be written. Also there's a difference between grinding because you know it helps you develop the skills you need/desire, let alone money, and grinding because some jackass doesn't know how to teach and assess knowledge.
It's also not about being in the zone every day, people can be "in the zone" perhaps a few hours per day, being generous, there's a whole discussion to be had about productivity in knowledge workers in relation to hours spent working in a day, there's a point where more hours doesn't correlate with more productivity, but anyway, I guess if I'm going to sum up my reply shortly it'd be something like:
Not all work is equally exhausting, not all grinds are equally tedious, and not all grind is pointless tedium, busywork teaches obedience not knowledge.
I can recognize grinding is helpful, but I strongly believe university falls on the "extremely inefficient grind" end, and I feel entitled to criticizing it when it's supposed to be in service of the students.