If number of undiagnosed neurodivergent people proves to be significant portion, neurotypical means just people who won the standards war of communication protocol
We never know the number of undiagnosed, many may be just capable of pretending but suffering.
Neurodivergent doesn't mean a failure at communication. That is a very reductive view of such a broad statement. Adding to that the concept of Neurodivergent covers a massive range of things. Someone who is ADHD faces different problems than someone with depression. So nearly everyone may be neurodivergent in some form but the average of communication falls within range of how we do now.
There are dozens (perhaps hundreds) of different mental models. There is a single mental model that is neither good nor bad that appears to to cover the largest number of living human beings on the planet. Because this covers the largest number of humans, it holds the title of the standard by which all other mental models are judged. It is the baseline. "Neuro" being "of the nerves" and typical" meaning "common". It is, by definition, neurotypical.
So OP continues the thought with: Consider instead of the mental model that is today's "neurotypical", that some other mental model was shared by the largest number of living humans. Would that other mental model, which could be drastically different, be called the "neurotypical".
The answer, clearly, is: Yes. Simply the definition of the term defines it so.
Neurotypical does mean pretty much exactly that, with only the clarification that while communication is significant, it extends beyond that.
That's a lot of why the terminology "neurotypical" and "neurodivergent" exists in the first place - because at this point, it doesn't even pretend to be an objective measure of mental health, but simply a pair of labels with which to describe the degrees to which people do or do not accord to current societal standards.
For example - posit a society in which it has become socially acceptable and even expected, when you meet someone, to punch them in the face.
If one were to ask a person how they feel about punching other people in the face, it's fairly obvious that the objectively psychologically sound view is that that's a thing they would not and likely could not do.
But to actually act in that way - to be unwilling or even unable to do it in a society in which it's the norm and thus the expected and sanctioned behavior - would be "neurodivergent." The conclusion would be that one must suffer from some psychological or physiological affliction that makes it so that one is unwilling or unable to act in a way that accords with expected behavior or societal norms. That one is "neurodivergent" instead of "neurotypical."
And in a way there is no "normal" to begin with. No one describes or thinks of themselves as "normal" when asked. Everyone in some way or another wishes they could just be Normal. "Normal" is what everyone else is, but not who any one specific person is - it's generally unachievable in a literal sense.
Neurodivergent people are not a homogenous group. You can be neurodivergent in different ways and it influences communication in different ways. It is improbable that one of the neurodivergent subgroups is frequent enough to turn out to be an overall majority. But you're not talking about majority, so what portion of the population would it have to be?
A lot of neurodivergent traits seem to be sliders rather than buttons, where it's only neurodivergent if the slider isn't in the middle. I sometimes wonder how many people actually have all their sliders in the middle.
I feel that people with mental disabilities/conditions have latched onto the medical "neurodivergent" term as a political "us against them" label. This can backfire spectacularly.