Also ‘The Cage’ establishes that the helmsman under Pike was a Lt. Jose Tyler and the CMO was a Dr Phil Boyce, who was then followed by a Dr Mark Piper for the first few episodes of The Original Series before McCoy becomes the doctor.
Dr M’Benga was the deputy CMO under McCoy - he’s present in a few episodes where McCoy is incapacitated and has to act as the doctor.
Why would he be the ships doctor under Pike only to return three doctors later and be the deputy?
Dude at this point if you continue watching you are just going to have to accept that continuity has gone completely out the window and that these are Star Trek "inspired" television shows.
You pretty much know that a multiverse is coming too.
Oh wait, I forgot there pretty much already is one.