I beg to differ, all mortars have tendency of squad wiping due to squad bunching.
True, hump-cover mechanics do make all squads fairly vulnerable to wipes. Even so, the 120mm seems to be more capable of wiping squads that aren't even in cover. This may, however, have to do with Axis squads being smaller than soviets, and this lack having that 5th or 6th entity straggling outside cover.
I note the 120mm wiping weapon crews with far greater regularity than any other mortar though, in or out of cover. But my anecdotal experiences are just one person's perspective. It's ability to wipe weapon crews is pretty obvious though. And that makes it an exceptionally challenging unit for Ostheer to combat.
My own 120mms when I play soviets almost always are wiped by offmaps, OKW stuka, or negligence to retreat after my front lines get flanked or otherwise collapse. Outside player error, it's most often offmap barrages and that bloody death stuka of OKW that ever takes out my 120.