Overall, taking all the portraits of Kublai, Marco Polo's account, and the typical style of Mongolian clothing into consideration, the surprising things about this Kublai are
1. He doesn't have a round face (Kublai's contemporary portraits - we have 2
existing portraits - all gave him a round face);
2. He doesn't have a headwear as well (Mongolians and their rulers usually wear their hat in the public, and, not to say, imagine not having any headwear on the windy steppe);
3. Mongolians around Kublai's time also have a distinct hairstyle (they shove their heads) and the hairstyle of the Kublai model is completely different.
Besides those points, he is definitely Kublai - having Mongolian clothing, having the same beard as Kublai, and, you know, Vietnamese rulers don't look like that.
I would say using the same head model of Genghis (which does have a round face) for Kublai's head should be adequate - Kublai is Genghis' grandson after all, why would their appearances look so much different? I do hope devs can, somehow, address these issues, if possible.
(I think this is also the first time in civ we have two leaders that are close relatives.)