Wow, your hours on preparing lectures, grant proposal writing, dealing with students, etc. are all way underestimated. A solid grant proposal that is likely to get funded (often in a super competitive field with maybe 8% acceptance rate) can take well over 2 months of solid preparation. Of course we don't actually get 2 months of solid preparation time, what with all the other stuff we have to do. My workload as an early career academic is roughly 10% on a funded project, 20% "research", i.e. grant/paper writing, 5% on a couple of committees I am on, and the rest teaching, with roughly half of that supervisions of PhD/Masters students.

For my masters students that equates to about 6 hours of meetings and reviewing their stuff over 3 months of their project. Most of my colleagues and I burn through that in the first month. So what do we do for the other 2 months? Well it's not like we can shut up shop and say "welp, sorry, but you've used all your allotted time" because that'd be terrible. So we continue to give whatever amount of time we feel is necessary (within reason).

Anyway it's not as simple as you've broken it down to be. Things ebb and flow over the year too, students need more mentoring at certain times of the year than others. Grant proposals, conferences, special issues journals all have deadlines and calls. My week is extremely varied and I'm still working on juggling all the different hats and priorities I have. I have a full load right now over summer even without teaching; when teaching starts up again I'll have to do all the stuff I'm doing now (bar masters student supervision) while doing roughly 25% of my allotted time teaching undergraduates.

Anyway, just another perspective.