Historical accurate? The previous unit are the mythical Amazons and you are wondering about how historical accurate the Companions are?

Well, a companion-like body of full-time elite riders existed not only in Macedonia but in the whole hellenistic world (hellenistic kingdoms, that is) at the timeframe of RTW, most probably though they were far from the known (Alex's) Companions not only in terms of value, but also in function and most notably, status (they were pretty much professional soldiers, while the older Companions were rich landowners-nobles that fought also).