that's understandable, I can see why you would have made it a high tier to reflect th power a shotgun usually is accompanied by, however 1 per second is not exactly slow, while yes compared to other weapons it may be in the scheme of a fight a shotgun is supposed to be the weapon you win with one shot and generally this is reflected with a slower fire rate if its a pump or lever action sort of thing, if it's semi auto it will obviously be faster but these have their own drawbacks one of which may be less damage.
Personally I'd suggest dropping it at least one if not two tiers as generally speaking you wouldn't be going toe to toe with a mecha even in PA, even though its sarp, cause we all know how strong mechs can be. It doesnt feel massively op but it has a feel of just a tad high than what you'd expect if that makes sense.
Again i'm interested in how this gas cloud is supposed to facilitate an electrical charge in a vacuum, and going back to damage again I'd like to clarify, the tier shot includes the affect of this electro charge as well correct? otherwise that's stacking more damage on top which would definitely be quite strong. This submission so far is giving me a Dragons Breath shotgun feel so i can understand the desire for higher tier damage. I'm more worried about in future however where some things may be misinterpreted or exaggerated if its not properly defined or regulated.
Another option i can think of instead of trying to get gas to stick together in space is having some sort of contained charge