And let us not forget that with most pop-up motors, once they have popped-up, you have to dive to get the speed
I’m a bit surprised by this statement. The five types with pop-ups, that I am familiar with, all have electric starters.
Concerning air starts, that is something I have familiarity with. I used to do checkouts in a Motorfalke. Although the starter was 100% reliable, we had to get the student to perform an air-start, which involved diving at 45° and accelerating up to nearly 80 kts before the prop would turn over. A lot of height was lost!