Considering that the Germans do not have infinite native shipments, they could get a new shipment of infinite Highlander or Riflemen, since they lack Musketeers.
Once they do the improvement of Wallensteins contract and reach the imperial age, the mercenaries will stop costing population (Since they don’t have infinite native cards), but will have a limited creation limit. This will make infinite mercenary shipments useful in the treaty.
A separate suggestion is that they enable the bayonet upgrade in the arsenal for the Germans.