And if a bolt pistol's end-game gear for your group, it sounds like you want to be very much on the gritty 'charge across no man's land into their heavy guns while using the remains of the last assault for cover' end of the scale. Which is all fine, fun, and in-character, but...you might want to think about having someone on hand to make sure they move in the right direction, maybe someone authorized to execute anyone running away...
It's not so much that simple fact that bolt pistols are "end-game gear" (which they are for Guardsmen), its that people forgot that Only War is about being Guardsmen. The whole concept of the game is that the PCs are just rank and file Imperial Guardsmen that are meant to eventually become the "heroes of the regiment" (which I believe it says somewhere in the corebook). Starting as a bad ass is contrary to the design intent of the system - and, to be clear, Commissars start as bad asses.
This argument, for me anyway, is just another version of the ancient debate between those that want to "earn" up to what they picture their character being and those that want to start there. Commissars start as a "set" archtype, as do almost all the specialists. There is no room for expanding, its simply about becoming a better version of what you are when you start.
In my opinion, shared by my players, Only War is about the process of becoming the hero, not starting there and simply living up to your billing. This is likely why the current squad is comprised of 6 guardsmen, with only a single specialist, who chose it at the request of the person playing the Sergeant. That fits the system and the fluff. My players would rather start as just another stick, but end up being a hero... or die trying. There wasn't much of a debate there. They simply gravitated towards it because, well... it seems clear from the materials and fluff that this is what you're supposed to do.
As for the last bit - about charging across no man's land - we haven't gotten to that kind of fight yet. I'm certainly going to eventually give them a taste of that lovely attrition war that the IG seems to love, but not yet. As a Light Infantry Regiment, they are not geared for line warfare. If they'd chosen something beefier, they'd have been doing that kind of thing from jump.