How the AI is working?

Hey, thats the first time i write in this Forum. Maybe its a bob question, but i dont understand, how the AI is working in case of training units.
I made a lot of “scenarios” for myself, cause i play that game out of “eye candy” reasons. I dont like competitive playstyle.
At last i created a scenario with Persians (player) and Byzantines (AI). Out of in my opinion historical correctness, i activated (and renamed) Imperial Legionaries, Imperial Zenturios, Monaspas and Serjeants for the AI side. But even on Extrem, the AI is only training Cataphracts and some Siege Units. No Legionaries, no Zenturios etc. pp.
Is there any possibility to make the AI training the other units as well?
I would be glad for some help how to change this…