Here are a few more suggestions
*Non-archer units should not pick up bows or the player should be able to lock equipment slots to empty. When non-archer units pick up bows, they often end up staying at rage and never closing for melee, even though the bows do no damage in the hands of those units.
*Since gnomes lack the ability to disarm traps, and the white knight keeper cannot develop traps currently, maybe the white knight keeper could have a different security system than traps.
Two possibilities are gargoyles and gnomish automatons. Gargoyles could be non-controllable, immediately fly back to a perch after nearby enemies are slain, could drop some stone on death, and there could also be a much cheaper version that is just a statue :). Automatons might wander around a set area, or rest at a charging station, but would need to return to a charging station in time. On death, they could drop iron. For lore purposes, maybe only gnomes should be able to make automatons.
I think that there are some pros and cons to having something like gargoyles and/or automatons implemented as opposed to having traps. During late game, traps would probably be deadlier (boulder trap plus web/fire trap on wood floors), but automatons and gargoyles wouldn’t need to be reset every time, and they could take care of weaker waves on their own.