I am genuinely bemused that there are apparently people who buy B4s and use them to snipe at single infantry squads.
In terms of munitions trade off this might be efficient, however the opportunity cost would seem very high - there will usually be better things to shoot at, and if there are not you have won anyway.
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I'm not prepared to comment on 2v2 mode, as I barely play that mode but I acknowledge that will be on smaller maps and it will be harder if not impossible to get out of the range.
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Really though the B4 counters OKW very well (uber tanks and fixed trucks), and OKW tend to lack the off maps that counter it.
OKH on the other hand have plenty of commanders with the off map abilities that counter on map artillery:
You get 3 commander slots
I feel sorry for those Ostheer players who have to waste one of them on such terrible doctrines as the list below in case they need to counter a B4
Close Air Support
Jaeger Armour
Joint Operations
Luftwaffe
Spearhead
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Really though, it only becomes good at Vet1 and then gets even better
Getting it to Vet1 in the first place is kind of a bother however