M39 In-game:
Semi-automatic firerate: 461 RPM (
7.69 per second), not 7.5.
If you are arguing that very few can reach/click that amount that is entirely different and i will not consider it in this reply as this can vary between each person.
Secondly attachments are very rarely considered for the balance of the base gun as they are limited by design to change/buff etc. due to their limited availability.
The M39 is meant to be used up close and personal, not at further range such as the rifle, and due to this, it has around 16% more dmg within its range compared to the rifle.
I also don't get why you are tying in injured marines as an example, the m41 still slows you down, the m39 does not, you just have a lower base speed due to the nature of your injury. The entire post you made is shifting the goal posts into what if's situations of "but in this particular instance the m39 is worse and m41 is better".
The matter of the fact is that the m39 is meant to deal more damage up close than the rifle, which it does, and deal less damage on further ranges compared to the rifle, which it does. You are entirely free to disagree in thinking the gun should behave this way but you will just have to deal with it.
Regardless of that, here is a snippet of the math i did back then when i tweaked the values around.
Attachment 1961
Attachment 1962