This became noticeable due to the quick kill of larger enemies. In fact, the damage per second of the tommigan became similar to that of the minigun (200 DPS). If the idea remains, then the minigun will not be needed anymore.
Viewing post in Serious Sam: The Sequel (Public Beta) comments
The change is just 0.04 second, so it can't be that significant. I just checked killing speed of tommygun and minigun and the minigun still got it beat. Again, this slight change was one way to counteract the weapon slow down bug (the laser and flamethrower also have this kind of change). But if it's really a problem, then I'll think about adding a slight buff to the minigun.