For the units alone.
Plus what hardcounters what is really irrelevant, it doesn't matter that Stuart hardcounter luchs if luchs have incomparably better AI performance with better AT support.
Stuart is 70.
Luchs is 65.
AEC is 50.
Basically, the less menpower unit cost, the more expensive it is fuel wise, so cost effectiveness is kept on correct level.
You want stuart to cost more menpower, then its fuel price would have to be lowered and USF would still get both, pack howi and stuart, just like ost doesn't need to choose between pak40 or pgrens and just can get both.
Doesn't OKW start with less fuel?