How is their current vet not already perfectly designed for a brute force AI unit? They get all the combat
Durability bonuses should be available earlier than vet 3 for an assault infatry and so should passive healing (if ti remained available).
Suppressive fire should not be available to the unit (cool down should go down).
Their 4 men durability is the only thing that keeps this upgrade balanced, removing that would be a mistake.
As I said reduce DPS increase size to 5. 5 men assault troops do not work that well. It should be obvious by now with ST.
Point here is that if they where a separate unit they could have separate tool set and vet bonuses tailor made for their role. Having and long range unit and assault unit using the same base stats is not a good basis.