Thanks for taking the time to actually make a test and sharing the results, unlike some other people.
How many test did yo do and at what range?
But what make think that a 300 manpower unit should be able win vs a 280 manpower unit with 120 munition upgrade to begin with? Especially since USF faction was designed to carried by riflemen and the come also come with snare (and grenades as some would say).
As for weapon upgrade I have pointed out many time that Penal are badly designed and if they are an "alternative infatry" they should follow PF design and start weaker and have to upgrade with a weapon.
Finally people retreat before the squad dies from small arm fire.
8 tests: mid range / green cover
Of course I would assume that a 280mp+120mun unit beats a 300mp unit. But lets keep two aspects in mind: Rifleman have far more utility on top of their damage and Penals have nowhere to go in late, they don't have the chance to get some sort of AI upgrade for munition.
A weaker start and a stronger lategame would be fine if you ask me. In early game they have quite a bit of power, but imo you don't really need Penals because Cons give more mapcontrol, scale better and have more utility. In mid and late game Penals can't compete with Axis AI infantry unless you get some weapon drops, so Soviet has to rely on Guards or Shock Troops. It would be fine if Penals would have a later power spike and thus could compete with axis stock infantry AI units later on, so that there is a more diverse approach to soviet commanders without Guards or Shock Troops.
Atm Penals have three problems:
1. Bleeding (and scaling):
27mp reinforce combined with only -15% received acc at Vet3 means that Penals will bleed you hard. All the way up to Vet 3 they have a target size of 1, at Vet3 they have 0.85. Any other similar non-engineer infantry unit has one or more of the following aspects: Lower reinforcement costs, lower target size, higher armor or damage reduction.
2. Utility:
There is simply none with the rare exception when you want to blow up a building or a bunker fast (if you got around it).
3. Damage drop:
Because they have no upgradeable weapons their damage drops harder with each lost man than it does at other units which keep their strongest weapons until the last 1-2 soldiers ("To the last man" doesn't make up for that).