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I'll start saying that the only change the current Bofor needs, is a barrage range reduction. Anything from 80 to 60/75 would do it. Cause this will make OH mortar "immune" to it's barrage.
I also think that emplacements in general, besides pounder, should require more input from the player. Once you know where and when to build them, there's practically no difference between a rank 10 or rank 1000 player.
Fixing the 2nd mortar from the pit but reducing auto attack to 100 (equal to 120mm and Leig) but leaving barrage range at 115 (as now) would be a good middle ground. IDEALLY we could also see light shells back (reduce damage but increase range).
Having said that, what i'm saying is that you approach the problem from the wrong way.
-First of all, it's the random issue. If you don't plan on carrying and trying to coordinate with your random teammate (remember that you are a random as well for him) your chances of winning are doom despite what type of opponent you are facing. When playing randoms despite of game, you are guaranteed losses which you can't do anything about it.
-You purposely focus on the long game, when that is an alternative, not the only way of playing as axis. You say you can't beat it as OH without tanks, but what about the early game? Osstruppen, sniper, 222, FHT.
Focus on what you can improve and do, rather than think that doing the same thing would work against all type of strats and opponents.