What disadvantages do camels have that horses are superior at? The only thing I could find in my (admittedly not super great) searches was that horses are less intelligent than camels according to this animal psychologist: http://www.thenational.ae/news/uae-news/forget-the-horses-whisper-near-the-camels which means maybe they are less willing to partake in suicidal war actions? They can run at similar speeds (clocked at 40) so the only other thing I can think of is that they aren't as easy to ride.
I'm going to do what I like to call a TSL (Tactics, Strategy, Logistics) breakdown. In essence, tactics is how well a military unit functions when it actually gets fighting, strategy is how useful it is in the wider context of a battle or similar action, and logistics is how effectively one could build and maintain that type of force.
Tactically, camelry does have the advantage of a higher potential top speed, but there is a key problem – look at a horse. Where are you sitting on a horse, and what is keeping you in place? Then look at a camel – where are you sitting there, and what is keeping you in place? Horses can be easily saddled, allowing a secure riding position, and one is closer to the ground, making shorter, less unwieldy weaponry far more viable than on a camel. Thus, armament is better and maintaining a melee is easier.
Strategically, camelry has no particular advantages or disadvantages compared to conventional horse cavalry.
Logistically, camelry really becomes rather unfeasible. Camels exist mainly in the Middle East, the "-Stans" and to an extent North Africa, which severely limits the potential for most cultures to develop them as military mounts. Furthermore, they have evolved for the desert and cannot easily adapt to other terrain, unlike horses, which, although evolved for grasslands and low hills, are capable of travelling the desert. Camels are also less common, and thus hard to breed in significant enough quantity to form a major component of an army.
I can't really do better than the U.S. army's historians, so will just place a link. https://armyhistory.org/the-u-s-armys-camel-corps-experiment/ The Ft Irwin museum also noted that the beasts were smelly, with a bad temper, and thus not popular with the troops.
Camels are more or less "specialized" to live in arid regions. If I had to make a guess, I'd think they could even have problems living in colder, more humid areas, but I do not know. The main reason, however, was that horses are more or less abundant everywhere across Eurasia, while camels lived (IIRC) only in ME area in ancient times and spread to eastern North Africa only with the Arab invasions, which means that camels could not have used in warfare. Camels did have uses in warfare in Middle East, however. I apologize for having no sources right now, but I am not at home right now.