Why though? If you wanted to compare the KV-1 and T-34/85, or KV-2 and IS-2 then you'd go ahead and compare these two units, not the commanders they're in, wouldn't you?
Depends. The problem here is that this mentality leads to power creep. For instance people where arguing that KV-1 need a buff because it a worse option than T-34/85 and the end result want KV-1 ending up being being OP and having to be nerfed.
Also, both the B-4 and ML-20 may do 'the same thing' aka lobbing explosive shells at the enemy, yet they are very much different from each other in many ways... in what way does looking at the commanders they come in help to analyze these differences?
No matter how they deliver their paylaod if the end result is similar a player will choose the commander and not the weapon.
Either these weapons will have similar use and the choice will be between the commander and not the weapon or these weapon will be design to do/offer different things and the choice will be more about play-style/map/personal preference.
Generally speaking B-4 is a hard unit to balance because big explosions have wipe potential which is simply too strong in game of unit preservation.
There many different solution for design of the B4:
Could be desinged cheap/less pop howizter more suitable for 1vs1
could be designed as AT oriented gun
Could be hard cap kills so that it would offer big kills but not wipes
....
Could be Ml20 close with different way of delivering payload but imo not sure this the best route take.