Lets be honest here pak howi while sometimes can do more damage then 120mm, its clunky AF to use, has hell of lot models for reinforcement and being decrewed with a lot more models being alive. But in any case, you rearely can play super agressive with your pak howi to begin with because of mentioned reasons, while you can do it with 120mm mortar since its generally just harder to lose it resulting more aressive placement therefore less scatter because of the range, so its actually questinable which of the units will deal more over-all damage during the game.
But in any case, even if theoretically or practically Pak howi is better in damage across the board, 120mm godlike (in comparison) survivability is not a fair trade-off, considering damage difference is not that huge as the one in survivability department.
IGs is cheaper I agree, but its cheap cost is the result of its perfomance, since its close to being useless unless using its auto-fire. But my point was that all three units 120\Pak\IGs are units in the same tier, I mean even 120 autofire was nerfed to be in line with them, so I think its kinda fair to look at them as a comparison anyway.
I'm just saying that there are more differences that we shouldn't forget when comparing these units. Survivability is definitely better on the 120mm compared to the Howie and ISG. The pop difference especially to normal mortars is huge (2-3). The 120mm should basically perform like 1,5 "normal" mortars. Compared to the Howie, damage is not really better, rather a bit worse. Especially if you consider that also the Howie has been reworked towards its barrage, which still reaches 20m further than the 120mm.
Clunkyness? I find both of them quite bad in that regard. The 120mm has a larger cone so it needs to reposition less often. But when it has to, it is basically useless. The 120mm needs 3 seconds more to pack, rotate and set up compared to the Howie. I assume this is largely map dependent. On wide, open maps with more flanking possibilities I found my 120mm constantly rotating to keep facing squads, that often run away or break through by the time the mortar can fire again. Howie can be similar, but I personally find it more responsive to enemy pushes. But obviously this is highly subjective.
I personally wouldn't put the leIG into the same "tier" as the 120mm in the sense of expecting similar performance. I find it closer to normal mortars, but in the end they all fill the same role so comparisons to all mortars are fine. I just don't want the discussion to drift to the typical "but unit A has this special feature which makes it too strong compared to unit B", all the while neglecting that there are huge price differences or something similar. Not saying you did that, but you get the point.