Yet during that time, the student doesn't learn much and the instructor doesn't teach much either.
Strewth
You should be learning and I should be teaching efficient pre takeoff checks, getting underway with a minimum of fuss and getting airborne as soon as possible. I would encourage you to learn your pre takeoff checks by rote and know what you are doing these things for and why without referring to a printed checklist (this does have its place too).
You may be learning at an airport that requires taxy time and clearances etc. Where I teach there is no unnecessary waiting.
I mean no offense when I say this but your comments show me, as an instructor, that you are a difficult student.