I think Landskneckts should just be made a unit with an “on-demand” function, as in, they change their weapons as per required scenario since they’ve been known to be versatile.
Baseline they’ve got sword as they have it now, thus they’re good at cutting down light infantry in area of effect fashion.
Incoming cavalry charge? Have them switch to polearms.
Got to take out the incoming heavy armor enemy units at the range? Have them switch to guns.
Of course, there needs to be a cooldown to weapon switching, and the gun usage should be reserved for Age 4 upgrade.
And of course, they need increased health to actually be worth something.