I knew people say this is very rare unit, that’s why they need to be rewarding in the rare case someone can do it in a competitive game. Also it is not extremely rare (like persian war elephant). Civs like aztecs tends to play heavy into monks and it is common for aztec player to do redemption. So xolotl warrior with aztecs is not uncommon.
However it is an extremely weak unit, missing bloodline husbandry and armour, 3 most important things for a melee cav. It also can’t be massed, you can only make it from converted stables. So it is reasonable to give them a buff.
My suggestion is give them 20 more hp to compensate for bloodlines, and get +2 melee and pierce armour to compensate for missing armour. Also the lack of husbandry means they are slow, just like teuton cav, so it is reasonable to give them a bit more armour. I think they can also get a bit of extra hp like 20 hp, once the player hits imperial age. Also they could make aztec and inca unique techs affect xolotl warriors so they get some upgradability also different flavours for each civ.