I am currently also playing a Hay campaign. I managed to get that reform. It seems that only through that reform you get access to the MICs that allow you to recruit the elites of the Armenian army, such as HAs, Armored HAs, Cataphracts, and even infantry- those nobles and the Armenian medium infantry. Which is the only way for you to have a succesful campaign. I managed to get all those regions required for the reform through my FMs and some slingers, but now they are not nearly enough. I am looking to stabilize my economy and recruit one cavalry-based army to take the east. To summerize: I think the Hay reforms just let you build better gov. types in certain provinces, which gets you better buildings and units.