Well, technically, it's not a theory. A hypothesis, a conjecture, but not a theory. A theory is a model, verbal or mathematical, that attempts to explain observations and predict future observations.
Outside of scientific circles, "theory" may very well be one of the most misused words in the English language.
At any rate, my conjecture about M'Benga is based on the fact that Babs is significantly older today than Booker Bradshaw was in the late 1960s, whereas the character is roughly a decade younger in SNW than in TOS -- IF there's only one physician in Starfleet named M'Benga. And on the fact that anything the producers say, anything the showrunners say, and anything printed in the writers' guide is subject to contradiction, even if it's actually filmed (literally or figuratively), until it appears in a release print (again, literal or figurative) that is shown to the general public. And on the fact that TrekLit established (albeit non-canonically) "Jabilo" as the given name of the TOS M'Benga. And on the seeming absurdity of M'Benga being CMO, then leaving the Enterprise completely (succeeded by Mark Piper, and then by Leonard McCoy), then coming back as a subordinate to the CMO. And on my own personal experience: a friend of mine is a retired gynecologist, and his uncle was a general surgeon (and from what I've seen, heard, and read, having multiple physicians in the same family is not at all unusual) .And on Occam's Razor: to me, having a younger M'Benga, possibly still in residency during the SNW era (or still in internship, or even still in medical school) is the simplest explanation.
As to Chapel, it seems simple enough, and believable enough, that a young woman would be working her way through graduate school as a Starfleet nurse, only to leave Starfleet to work with Roger Korby, with Chapel and Korby subsequently falling in love. Korby disappears, and Chapel returns to Starfleet, and the Enterprise, in hopes that she might one day find him. And when she does, she ends up wishing she hadn't. Then eventually, she goes for her MD.
And I can certainly see SNW Uhura developing into TOS Uhura, and eventually TOS Movie Uhura.
I loved Scotty's appearance in this episode, and I love how, for the first time, he's actually played by a real Scotsman.
And especially given what was discussed in the "Gorn" featurette that came in the DVD set, I see no reason to write off the SNW Gorn as not being "the real Gorn."