I don't generally use horse units much myself, but the Aysas are a lot better than they seem, particularly if you get the 100% withdrawal chance. I was able to use them to flank and kill spearmen pretty much without retaliation, and the ability to build them without Horses means you can have a defensive army that's pretty much unparalleled in the early game.
I just assume you are referring to the Tnoy otherwise you are talking about the Spear/Pikeman. Which are great. You can use them like celtic chariots and rend units to death. Retreating doesn't really kill units tho, so something has to come in there and get rid of them.
It's like one in four that you get Liquid moon which would then be the "good" one (or best one or whatever). Out of 15 units I have 3 with Liquid and only one of them is a horseman. While it's good it doesn't change really that you can really only hit a spearman once, twice is pushing it and then you better get away if you want to live. In that regard it would probably be better to have Crushing sun so you make that big first attack and then you can bugger of to safety and healing. So while it might be nice with Liquid moon you can't really build an army based on a one in four random promotion that may or may not be equally distributed, it probably is I have not checked the code or anything. That said I'm sure they'll be better as Knights.
In some regard I'm more in favor of Guiding Star so I get the extra movement. I have gotten that on a fair amount of Aysas so they are very fast in that regard.They are far superior to the Tnoys (not only cause they are pikemen so they have a higher level in that regard).
That said I had to resort as per usual to rename the units so I know which has which promotion as I don't fancy looking at little icons to see them when I can just see big bold text instead telling me.
aysas crush x2
aysas guide x3
aysas ram x1
aysas liquid x1
tnoy liquid x1
tnoy ram x2
tnoy guide x1
scout liquid x1
scout ram x1
swordman crush x2
(+ there are a couple of compbows and catapults to but since they don't get promotions they are not included)
But (Crush 4, Guide 4, Ram 4, Liquid 3) so it seems like an even distribution, one or two or three units have died so I'm not sure what they had but I doubt it would change much.
(edit) Liquid doesn't translate into extra movement when disembarked but that is probably normal and working as intended.
That said I restarted (for version3) and decided to tweak the world a bit to create more of a desert world (to fit the civ) and that turned out to be great. Perhaps so cause the AI is so bad at it. I have already laid waste to two rivals (Sweden and Austria) and I just entered the medieval era. So it's not that it can't be played with or is bad like that, it's just horsemen are not the backbone of any army. That said I do have four of them but they seem to mostly just be there and they are not really doing much -- one attack and then off to heal. They bulk up army score in some sense but they don't become "good" (or safe) until you can get Stalwart on them and that is some far away promotion in most cases (but not unobtainable if you just follow the city-state conquest quest path).