There are only two kinds of citizens: Naturalized citizens, and Natural Born citizens. Since you concede he is a citizen, and he has never been naturalized, he is thus a Natural Born citizen.
We are in agreement. Perhaps here’s another way to get through to doubters:
Suppose both of Cruz parents were US citizens....he would be natural born. Correct ?
Since there is no provision that specifically says two parents are necessary in this case, it would be logically construed that one citizen parent is sufficient.