Ok thank you for your detailed answer. So does it help speed up the process though?
My view is that it does not - usually anyway - speed up the process to do medical before it is requested.
For most applicants, medicals are not the reason the file takes longer. It is early in the process (most of the time) and other things like security clearances eligiblity etc come later and are more unpredictable.
Plus, sometimes when applicants do upfront when it is not requested, there are delays caused by doing it outside the process - i.e. they can;t match the file etc.
Now there may be some specific circumstances, but most of the time - don't do it.
BTW you can watch how most files progress - they get AOR, then biometrics request/medical request close together, and then.... a long period of waiting while IRCC does their stuff internally. And no, they don't 'wait' for the medical to be completed before starting the next steps, only for the last decision steps. (This is visible in the gcms notes that they don't wait)