Matchlocks are not overpowered...except if u make a lvl 9 Monk version with 150 range, high loading skills, rapid fire and using stand and fight plus inspire.

You will then get a tommy gun!!! Other than that, you can (not easily but can) counter them with archers, cav charge covered with targets baits(ahsigaru)
or do not over commit(bad habbit of mine) your infantry into the main clash and go around the line or gaps to finsh them off.