And still 4 models means 5 if this was a regular mortar, since you need to kill 4 dudes to actually decrew it, but this is a start.
I also think that OST counter barrage should outrange the 120mm, currently it is 100m range same as barrage range for 120mm. For example 120mm even with that scatter has a very high chance of wiping OST counterpart (albeit with slight afk from the OST mortar), but not the other way around. Maybe give barrage same range and add give it back with veterancy. Even with 80 range it will have plenty of lethality.
Well as I was saying, some of 1v1 and 2v2 maps are more or less open, but the mojority of maps still providing you with either destructable or indestructible sight blockers allowing you to get 120 closer to the pottentual bombardment zone. Meaning that realistically mortar duel very rarely happen at max range to begin with.
Not to mention that (even judging by your video) barrage\delayed fuse of 120 still covers like half of map to begin with, and the 120mm was staying near its base, so realistically there is no way you can kill it to begin with. While Schwerer was placed aggresively (which is imo mistake made by OKW) its still impossible to repair it and it impossible to force away 120mm anyway.
And counter barrage is questinable, at best you will be able to direct hit it with first few shells and force it to retreat, but usually (from my expirience) 120mm mortar in general need like 2-3 shots to force retreat enemy inderect. But even with it, soviet player can just use barrage of his own against your mortar so CB arent solving anything.
On top of that in teamgames soviets can also pair with regular mortar and spam flares increasing 120mm mortar accuracy. I've lost so many squads to it, just because of its burst damage when they are paired, one landing near downing squad HP to like 20-30% with an instand follow up which is just wipes the squad.
In other words oppresive AF, I think right now the only way to counter it somewhat you either need to use Mortar HT as ost or zu-fuss as OKW, or maybe somehow survive untill LeFH.
My point is, if anything 120mm mortar should be a glass cannon (just like USF pack howi), it should be hitting hard, but it shoudnt outlive everything and be immune to other inderect units which are awaible at ~2CP mark.