The difference is that Trajan is one of the top picks of Rome. I'd put him 3rd behind Augustus and Julius. No, Byzantine leaders don't count since Byzantine is a different civ so yeah, Trajan is a top pick. But yeah, since Julius and Augustus has already appeared in previous civ iterations, Trajan being next in line is very much justified.
Wu Zetian on the other hand is a different story. Two of the universally greatest Chinese emperors: Tang Taizong and Han Wudi hasn't appeared in Civ yet. Not to mention several others: Yongle Emperor Kangxi Emperor, Wen of Sui, Liu Bang, Zhao Kuangyin, Xuanzong of Tang, Emperor Qianlong, Emperor Yongzheng all have better contributions to China than Mrs Wu. I think you need to go back to our previous post. My point with Wu is that China has too many great Emperors to choose from over her. If you think her pick was justified, the only possible reason is, what Zaarin said, her gender and nothing else.
As I have mentioned, pure "greatness" comes next, in my measurement. We are not holding a "greatness" contest so clustering all the great leaders in a package should not be the priority.
Of coz I wont disapprove Taizong, but neither will I disapprove Wu.
her gender and nothing else.
And I hope that you come into realization of this:
Showing leader of another gender, rather than they purely being that gender, is also a showcase of another side of a said civilization.
Opposite gender means different clothing, language usage, appearance, different fascinating background stories, etc.
NOT ONLY JUST BECAUSE HE/SHE IS OF A CERTAIN GENDER.
"choosing a certain leader purely due to the gender", is nonsense. A gender contains more staff behind the curtain.
A civ already with a male/female gender has a higher priority to get their gender counterpart, to show off another side of their culture/history, although this is not compulsory.
Miss Wu, or Mrs Lee. Wu was her surname, not her husband's. Her husband(s) was Mr. Lee(s).
Also, try looking at male Chinese emperor pictures in google. You'd be surprised how different their clothes are.
Since you mentioned, lets make a comparison between male and female royal fashion in ancient China, using some of your mentions of the great emperors.
Lets keep Qin as the original model of comparison:
We can clearly see that the male royal dress was 90% similar to Qin's style, roughly before Tang Dynasty (where Taizong was).
And from Taizong onwards, the dress code became yellow gown with narrow sleeves, and a black hat/crown.
Their private/less formal clothing maybe different and dynasty dependent, but the royal court dress,
(especially the coronation dress, which was the most iconic and lavish) was surely sharing a similar dress code.
And for females of the same era:
Didn't add Yuan (Mongolian) and Qing (Manchurian) dynasty as they were not ruled by Han chinese, so their dress codes were drastically different and not appropriate for comparison.
Thus which gender has a more distinct fashion evolution in ancient China?
I will let the pictures argue for me. But I hope that you should go-google more yourself.
It will be such a loss if they only include male leaders for China, losing the entire set of beautiful female fashion. Therefore, why not let Wu take the responsibility, when she was also a great ruler by her own right.
), helped instill Zen Buddhism into the warrior class, and in general acted very competently during his rule and never backed down. Over all, not a bad choice, if, again, a bit obscure.
)
I'd like to think the Maya are inevitable as well, being far more important than the Aztec (they really ought to be a base game staple), but the New World doesn't seem to be much of a priority to Firaxis--no indigenous civilizations in the base game, Aztecs as day one DLC, and it took us until the first expansion to get a civ native to North or South America. 
Hopefully neither the Cree nor the Mapuche will be the sole representatives of their continent. The Cree might be (though I hope not), but I don't think the Mapuche will be.
