My understanding is that the sprites for this game are made with 3D models which are then animated and rendered into 2D sprites.
To make it easier for modders to create new units I would ask if the devs could release the original 3D models files for all the unit models so that modders can easily edit them and/or switch-out animations in order to create new, quality unit models.
You could make stuff like Dismounted Mangudai or Mounted Teutonic Knights, or units which are composite parts of other units.
I’d hope the devs consider this.