I always thought of the B4 as similar to axis units such as the jagdtiger, tiger ace, and king tiger: it is one of the pinnacles of soviet power, and meant to be a feared end game unit.
As such, I think it would help if it was treated that way. I would say raise the CP cost to 12, and fix the damn direct fire ability since its a bugged and useless waste of munitions, especially since the precision shot basically does the same thing, costs less, has larger range, and never misses (the direct fire shot does miss and will explode if it hits a shot blocker, like a wooden fence or a blade of grass).
It really is probably the most powerful unit the soviets have (other than the ISU-152) and it was obviously meant make axis players shit their pants when they see it. If you nerf it, it just becomes another boring unit which everyone will probably skim over and forget. If anything, increase its price or CP cost like I mentioned earlier, or do something to lessen some of the RNG.
At least be grateful we dont have to deal with the B4's sister, the 280mm BR5