Princeofnigeria
The illustrious
Just to play devil's advocate, couldn't you argue that any unique unit not requiring horses gives you the option of selling your horses (assuming you don't want to use chariots or horsemen in the first place). And also, if you simply don't have a game where you are building the temple and/or haven't yet reached the tech that unlocks temple then isn't that the same as allowing you to field more units? I don't know, your last point about speed is the only one I can get behind.
Well, good question! Other Uniques do give you this advantage, but the war elephants speed (or lack thereof) makes it a more defensive unit, and the the hunnic Horse archer, while better, lacks some of that speed (but makes up for it in terrain movement) is a much better city attacker than a defensive unit. I say the chariot archer is good for quick, precision strikes at the enemy, using (in this case) numbers and strength to make up for their fragility. And as for the burial tomb arguement, you could say that about not building any building then, that it allows you to build a bigger army. But here, you can still maintain your infrastructure AND get a quick big army, also having faith in that era is VITAL. As well, the +2 happiness works well on defense (+1 culture for two happiness, AND +10% gold production) and keeps you in the green on offense.