Sauro's strength lies in their horse's numbers! They have easy acess to the cheapest horse archers ever (in terms of both recruitment cost and upkeep), Sauromatae Fat Aexdantae, at mere 1000+ Minai and about 250 minai upkeep... they could ammased in great numbers compared to their Saka and Pahlava counterparts, not to mention that they are also mercenary so they could be levied quickly if sorely needed... compare with Duna Asya or Pahlava Shivatir, maybe in small 3 or 4 unit, that doesn't matter too much, but when you have multi stacks of HA army that need patrolling all the Steppe.... their difference in upkeep will matter a lot, especially if the economy was tight! Many Sauro Variants of the Nomad units are also cheaper, with just sightly less performance, just use them as Zerg version of Nomads.

Makedon and Epeiros have acess to Agrianikoi Pelekuphoroi, among the best assault troops to be employed against seleukid cataphracts on foot (read: TAB). And the makedonians has acess to Hysteroi Pezhetairoi, maybe not a relatively good units when compared to Argyraspidai or the Crack Chaonion Agema... but at least they have an incredibly large AOR (even to the extent you'll babysitting the Romans for march of time) you can just train them virtually anywhere in the mediterranians...

Epeiros has better choice, the Molosoan Agema is the fastest heavy cavalry that you can use not only for breaking enemy formations, but also to riding down skirmishers and still have enough stamina to impale enemy general... also the Chaonion Agema is the top-crack phalangitai by stats... they beat everyone and with acess to experience inducing temples, they become killing machine by birth... and the last thing wonderful with Epeiros is.... They can train Elephants at Ambrakia!!!! Means the Romans will get many fresh elephant meat if they carefully use their leves and velites, or become a smashed sticky meaty sauce if they aren't.

Pontos gaining extremely wide kind of units, that wasn't particularly good, but you did have every counter for everything your enemy is about to thrown at you...

Hayasdan? They had horse archers and catas while they are civilized and didn't get their reforms as hard as Pahlava does (you just build some market and then change the gov't type). They are basically a civilized nomads with inclination to massive archery tactics (having Kovakasi Archers available at the start and in nearby regions means that those cheap but damn good archers are about to be ammased and made the sky dark with their arrows)

Saba? At least.... they have really isolated position and they have mines in nearby settlements, just play turtle and you can build up your force. But actually, this faction is among the hardest of factions available........