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I've tried out the new B-4 in the commander revamp beta and also got somewhat mixed results, so i dug a bit deeper. if you visualize the old vs new aoe profile, the reason for these underwhelming results - especially against vehicles - becomes pretty obvious.
Vs infantry the new b-4 actually performs pretty good, if not better than the live version. As you can see from the graph below, the AoE damage vs an 80 HP target (solid line) is roughly comparable to the old profile; the lethal radius shrunk quite a bit (from ~5.6 to ~4.2 m) but the minimum damage dealt per shot went up from 32 to 45.
So essentially the new B-4 kills slightly less on a per-shot basis, but deals more overall damage to anything caught in its blast radius. plus, it is now guaranteed to drain more than half the total HP of any infantry model, allowing it to 2-shot squads that stick in the danger zone for too long.
That is, unless heavy cover is involved. Indicated by the dotted lines, the damage drop-off against targets with higher effective HP (160 for models in green cover) is much more pronounced than in the live version and, in fact, even inferior to that of the ML-20. The 160-HP one-shot radius in the beta is only ~2.2 m versus the 9.4 m of the live B-4, which isn't even in the same league anymore.
But it gets worse. If you look at the whole AoE curve (graph below) it is immediately evident that against high-HP targets, such as vehicles and emplacements, the new B-4 offers little more than an average howitzer shell.
Outside of direct hits the chance to deal any meaningful damage vs these targets is vanishingly slim even compared to a ML-20 shell. The fact that the shell count is increased by 3 doesn't really do anything to remedy that, so it's safe to say that the AT and anti-emplacement capabilities of the B-4 took a massive blow in the beta.
I'm not sure if the new AoE/damage profile also applies to the direct fire ability, but if so this would make the ability virtually useless as well.