It has to do with shock modifiers, even if maurician has better overall pips, charge infantry has more shock and at that current tech i believe the infantry shock modifier is bigger than the fire modifier. Your regiments will end up doing more damage(and taking less) if you use charge. With that said they're both quite similar. I don't really know any of the numbers off by heart but I remember in Eu3 you would get charge when you unlock, but then change back to maurician once the fire modifiers caught up.