Both those are walking a very thin line. M'Benga could have been a CMO without the name. But, on the other hand, we know next to nothing about those characters and I have feeling they feel like M'Benga will benefit like Pike has.
Time alone will tell.
Yeah, but with M'Benga, you don't have to come up with a reason why he's younger and of lesser rank/position by the time TOS rolls around. You could simply do what you want with the character of O'Benga.