OpenRA

This is of course a bug and there should be a solution for it.
I think the best way would be if the troopers shoot on the target but the zapp will be stopped by the wall and damage it,
Then the balance complainers would be calmed down as the troopers are good wall shavers.

My idea on balancing Tesla troopers has been explained far to many times. So im going to respond with the wall one.

Tesla troopers zapping over walls is fine IMO. Balance wise Allies have an arsenal of units that can counter Soviet infantry. (Chrono tanks, Tanya, Hinds + Hind crash, Artillery) are some examples.

As for logical means I would say lightning can strike anywhere and loves to strike metal surfaces. So you can fire a lightning strike up into the air and it can jolt down to the metal surface such as a vehicle or infantry holding a weapon. Technically as well since lightning strikes from the ground up meaning coming from the tanks metal surface to the weapon.