Well as far as camel archers go, (all mounted ranged units for that matter), If your main rival is Siam, don't bother building camel archers, just when I was getting my unique unit out, Siam who must have teched to chivalry earlier declared war on me and he had his UU, the Elephant with 22 str and +50% against mounted units, my camel archers only did 1 damage to his units, so I had to give up on those and go for cannons to defend asap. Also those Beomoths can take down a city at that time in 3 hits, so I lost half my empire in that war, and only saved myself because a city state gave me a great general and I spawned one too, so I placed two Citadels around one city and held them off.
Also having a militaristic ally is cool, twice mine came through for me. I was preparing to fight japan when he had early domination of the continent, I had an okay army, 4 archers 2 horses and a swordsman or two and a couple catapults, but Japan still had way more troops, but he was busy attacking my ally the city state with the majoirty of his forces so I declared war on him, partially for attacking my ally, and partially because I wanted some puppets, and while the majoirty of his army was stuck trying to take on the city state, which are always harder to conquer than a normal civ's city. I took out all the rest of his forces, eventually helped protect the city state somewhat, and enough cities for him to surrender.
Then again when Siam declared war on me, when he got far enough into my territory one city I had held a choke point off from the majoirty of his territory keeping over half his forces at bay with 1 treb then cannon, mean while I lost a few cities behind it, and would have no doubt lost the choke point city but my city state was right next to it and legions of forces attacked him instead, but again I helped defend him where possible until he finally fell, which kept my choke point alive long enough (it eventually fell under superior forces from not only his side of the city but my own as well (which had been taken over). But this was long enough for me to set up a dual citadel protection with pikemen and eventually infantry, I was really close to fighters at this point and I held him at this last line of defence till I built them, and then I went on the offensive with fighters backing me up, took a few cities back before his re-inforcements pushed me back to my defensive line. Where I held it, using fighters to decimate anything foolish enough to come forward, and then he sent some anti-air units in, and I decided to expirement with the air fighting some more, (note : don't attack an anti-air unit, unless you have air sweeped all of the anti-air units in range, the anti-air units will kill you without even a fight.)
But he never sent ground troops in with them, so I just killed them with my own ground troops and citadels taking 3 hp, and then it was just about waiting till utopia was built.
Anyway, thats my little story of why using Camel Archers against Siam is a bad idea, but I do agree, they are pretty cool, if I wasn't facing Siam they might of been useful to me. And Militaristic City States can be worthy allies.
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Oh and when I say "I helped protect the city state" thats not quite true, the only two times it really came through for me, by being the target of enemy assault pretty much, was when the enemy had conquered my cities surrounding him, so the enemies cities were between what forces I did have and my ally. Fortunately the city state gifts units, and these are what I used to help fight off the units that attacked him. Suffice to say, he did most of the work protecting himself, and he was pretty good at it, for example when I declared on japan, my forces were barely more than my city states army, though his was a more defensive army of spears, which as I said really held up most of japans forces, they really are worthy allies if position in a place to help, they won't ever send their armies out to attack, or rarely do. So more useful for defending a position.