Pahlava isn't that hard especially as they have a good economy(once reformed) AND a horse archer army which is very potent with enough patience, imho definately easier than saba and bactria, especially(compared to saba not bactria^^) in late game where you have(and can afford) amungst the strongest units availible plus a somewhat decent infantry division with hellenic and eastern infantry. Sauromate are not that bad either but don't have nearly as much potencial as practiacally all factions but the saba.
this only applies for people who like to use horse archers, like myself - supporting a halfstack of tracian and Skythian light cavalry as the KH in my first campaign whereas I really suck at using phalangites :(

ps this is not directed towards you, WinsingtonII but more the general opinion that pahlava is more challenging than Pontos or Bactria, personally I'd even rate Pontos more challenging than Hai because of their general fighting style but on a more subjective level they seem pretty even to me