These 2 specifically seem especially over the top, even considering the overall power of T4s.
Mortar: Damage reduction. Maybe increase minimum range, and obviously fix the ‘fire on yourself by aiming straight up’ bug.
Shield Drone: Any one of the following-
Add a deployment cooldown, so it can’t be dropped immediately after it is destroyed.
Decrease battery size.
Increase recharge time.
After draining, add a minimum amount recharged before it activates again.