Because you have to be one bad mofo to run around in a war zone with nothing but a pistol like an Imperial Guard commissar. I'm also hoping that they'll finally give the soviets a commissar equivalent. Why has this not been done yet?
Who? What? Where? How?
Whatever a "tinner smg" is - Penals have SVT40s (rifles ). And trust me, even with the 1.5 armor, a pg squad would still chew up the shtrafniki. It would just take a bit longer
The problem is that there is nothing about this unit that justifies its cost. The dps bonus from the SVT40s is negligible - you're better off getting two scripts for 480 than one penal squad for 360 (the two squads will give you more capping power, twice the effective hp, i.e. staying power, and more dps). You're better off using flamethrowers on your engies and the satchel is a sad excuse for an explosive device in most cases - bunkers and caches are not destroyed by them.
An armor buff to equal the armor of grens and pgrens would make this unit slightly more viable consequently making it an early non-doctrinal counter to Ostheer infantry blobs (something I've been encountering a lot more often since the tank scatter increase).