The phrase you get thrown around with regard to starts is normally ‘triple extension’, and not everyone agrees 100% that it’s necessary.
I think what Dr. Mann says in his book is relative, in that excluding the first initial ‘push’ out of the blocks, every step from number 2 to until you finish will be roughly the same stride frequency. So you (should) reach maximum turnover very quickly.
But obviously the difference is that during the start, the steps will naturally be shorter because of the slower speed. And what I think he means is that you should concentrate more on getting all the steps in, rather than ‘reaching’ for a long stride, which will slow you down.
I’m very familiar with Ralph’s work and have worked alongside him at workshops where he’s delivered that to coaches. He definitely teaches high frequency during acceleration. This is not the way I teach it though and prefer bigger more complete pushes. That’s not to say the turnover is slow, but from a conceptual standpoint I have found it far more effective when athletes push back hard on the ground as long as possible.