@Raz
Legionaries actually are not weaker .. they have good stats but comitatenses being the mobile force will have higher attack/charge than the legionaries ..
About the cost of the units .. legionaries are expensive .. but comitatenses will be even MORE expensive .. this way the comitatenses will be elite force they were in those days ..
what I've read(this could be wrong off course) is that the numbers of the comitatenses were small and thats why I would make them difficult-do-get-unit ...

Now ..
About the progress ..
Real life(yes .. I do have it) makes some limits to the progress of this mod ..
Also ..
I have no fresh ideas
So .. I would appreciate any help I could get