The Hetairoi Is my favorite unit as there are so many positives and no meaningful negatives. You will receive 25 science per unit when built in your Basilikoi Paides, starts w/ 1 promotion, moves 4, does not require strategic resources, 46 operational melee strength when accompanied with a great general, +5 great general points for every unit killed (including barbarian scouts), available early in the tech tree with horsemanship. Heavy cav unit that upgrades to knights/tanks.
The opening promotion allows you to slam a couple of them into a city then promote and fully heal just and the science you earn for for producing them in your Basilikoi Paides can be invested into stirrups for an early knight, but who needs ‘em. And don’t worry, if you don’t already have a great general from building your Basilikoi Paides, you soon will. As each unit killed (including barbarian scouts) gets you +5 great general points.
I think these saves from my most recent Macedonian game augment and highlight what I’ve said above; demonstrating the devastating effect these units can have over a very short period of time.
Here’s a summary of the game:
The Mapuche were completely out of control, orchestrating a successful war against Indonesia as well as developing their districts effectively. They had a 40 science per turn compared to my 8. They had 25 culture to my 9, and 8 cities to my 3. The Mapuche cities also had high adjacency bonus, developed districts. I had one Basilikoi Paides, Magnus, a gold horde I had been saving, allot of real estate to chop, and the ability to create Hetairoi.
An Emergency against the Mapuche came up, I figured, what do I have to lose?
31 turns later, the Mapuche war officially morphed into a mop up operation.
After another 16 turns, due to the high movement rating of the Hetairoi (4 normal and 5 with a great general), I had traversed back across the Mapuche land I just conquered to address the next most serious threat, Montezuma.
Over the next 47 turns I knocked off Montezuma 1st, then the Germans, then the Khmer, and finally what Indonesia had left after the abysmal ancient era shellacking at the hands of the Mapuche. The victory screen flashed for domination victory 8 turns before the close of the Classical Era. I don't think this would have been possible on this map with any other unit, as by the time I would have been able to make, say a Mamluk, the Mapuche would have further snowballed out of reach. Infantry units just don't have the movement, and naval units are limited in scope, even the fast moving Nubian archers could not have swung it (not even close as their movement is not augmented by Classical Era great generals).
I began the Classical era with a 19 era score, needed more than 32 to avoid a Dark Age, and between 33 and 44 for a normal age. Due solely to the early advent of the heavy hitting Hetairoi (with the horsemanship as opposed to stirrups), I was not only able to avoid being overrun, but was able to achieve a domination victory 8 turns before the close of the Classical Era, I had 139 era score.
I’m not all that sure Gilgamesh's fabled warcart can compete, as he has to cool down (or risk getting his carts killed in droves) until he can research stirrups (that’s assuming he can find any iron). A knight upgrade is nice for the Hetairoi, but by no means required to carry on with the conquests (just stay within range of a great general).
You did ask.