They used to be.
The role of each unit does not really matter as long there is room for both of them in an army composition and not having to spam on or the other.
Penals are intended to be optional and an alternative to maxims or elite infantry. cons are intended to be used in number all the time. It's not really comparable.
Penals are being treated like mainline infantry because cons arnt up to the task, same reason maxims used to be same reason snipers used to be.
And saying that all mainline infantry fill the same role is ignorant of design, it's like saying brass knuckles and bazooka fill the same role because they are both weapons. Penals and cons couldn't be more different if toy look at their stats and vet and are clearly intended to be used entirely differently.