I can't say about Gachi, but in my opinion the lethality on this unit is too much.
I would say that either keep the lethality but make it significantly easier to counter it with inderects, so at least agressive or careless placement of it would be punishable.
Approach of nerfing its cost\timing is also can be chosen. Timing is especially broken, because its super easy to just play untill 2CP just with cons\penals and then call in 120mm mortar.
But the question is, by how much you would push it? You can use ST aproach and push it back by 2CPs, making it 4. This would make it significantly harder to play just with inf into strate 120mm mortar, but imo, it wont solve the problem unless you are not badly loosing.
For 1v1, yes it will nerf it quite drastically, but its questinable if it will do so for 2v2+, because even with 4CPs, ones it hits the field, even by 4CP timing you wont have any real counters to it.
Sure you will have more established army and maybe you will be able to snowball based on that, but if we imagine that the game is 50\50 then there wont be any major changes.
Well for OKW it will be easier to deal with it, IF OKW decided to rush zu-fuss, but if he dont, nothing really changes.
And ofcouse its perfomance can be nerfed aswell, but since its a last coh2 patch I woudnt risk it, coz we can end up with useless unit.