Penals with AI weapon upgrades are actually very strong, coincedentally they were never given any by default(almost sounds like a biased balancing team), double Vickers K from the UKF M3 actually push them into elite infantry territory and that strategy was REMOVED by the balancing team with no explanation.
While it was kinda funny when (arranged) teams pulled it off, it got removed because it was broken.
The combat veterancy with then double 1.3 accuracy multipliers (now 1.3 and 1.2 at vet 2 and 3 respectively) is clearly not designed with weapon slots in mind.
Almost +70% dps at vet 3 and double LMG turned them into absolute terminator squads that won every fight with ease to a point where it was hopeless for axis inf. Some people even took that a step further and spammed "For Mother Russia" with then +50% accuracy
It was as bad as when Conscripts had 2 slots or when the +300% accuracy cover bonus from Osttruppen applied to their slot weapons with 0 penalty