I don`t think that the matchlock unit in itself is too strong, the amount of kills including FF is ok. The only thing they need to do is a moral shock for friendly troops, too...and even a bigger one than for the enemies. The enemy sees the guns and expects to be shot at...friendly troops don`t do that and for being shot from friendly troops into their backs the moral penalty has to be even bigger.
If that tweak would be implemented matchlocks are no fire and forget unit anymore...you would have to expose them, thus having to protect them and the most matchlock abusers won`t pull that off because they lack the skill imo.
I would like to see that in the next patch, tbh i think they _must_ do something like that.