Not sure I'd say "bad" per se, but definitely not worth the money - Armenian cataphracts (can probably generalize to Parthians as well). They're very capable, but very expensive. And the key point is that the cataphract horse archers are available one MIC level lower, for less money, and equal charging ability. The pure cataphracts just get you a melee weapon (IIRC armor is the same, at least for Hayasdan). Add to that the widespread availability of Kinsmen who are the best non-cataphract heavy cav in the game, plenty good enough to form the cavalry wing of an eastern army, with a cost around 60% of cataphracts. Not much point other than eye candy/flavor/RP to pay for the expensive pure cataphracts.

Relatedly, the Armenian Noble Infantry. Same stats as veteran Shipri Tukul (3 chevrons, IIRC), with less convenient recruiting cities and higher cost. And the ST can be recruited as mercenaries for extra convenience.

Armenian Skirmisher Cavalry - by the time the player can get these, Hayasdan will almost certainly control at least one of Kotais or Mtsheta (or however you spell that one). The latter both allow Scythian horse archers from a regional MIC1, which means all jav-cav in the realm are obsolete. A similar argument can be made against the Dahae jav-cav further east.

Velites - unless they've gotten a lethality upgrade on their melee weapon since I last looked at them, they're just understrength leves/akontistai with a couple more points of armor. Leves/akontistai are the way to go for javelin-tossing, Peltasts can fight well in melee, last I checked Velites were mediocre to poor in both roles.