Blitz Needle (and the other type versions of it):
The gunner version adds to an already powerful gun by making it draw more quickly when firing, and making you walk faster. The change would definitely make people with blitz needles very happy, but I feel the change makes the gun too over the top. Since it's probably the best gun in the game, it makes sense to have the drawback of a slow draw and a slow walk so players have to fire this powerful thing carefully. If I used the gunner version of the blitz on vana I would have a much easier time than usual, which does reduce the difficulty of not only this boss but others as well.

If these changes are put on a blitz I wouldn't complain though since I am a blitz owner and would enjoy them very much despite the concerns.

As it relates to swords and bombs, it's already powerful enough as it is, the gunner version goes beyond that.

Valiance:
The gunner version has small bullets as opposed to the big bullets of the traditional valiance. It would be strange to make this change when the alternate damage type valiances have the big bullets of a normal valiance. The change is superficial so there's really no issue here.

As it relates to swords and bombs, no change.

Callahan and Iron Slug (and the new versions):
All the changes here are great. The both had more drawbacks than the blitz needle making them not very desirable. Particularly how the player would fall down after a charged shot. The gunner versions fixes their drawbacks making them more competent weapons. They shoots just slightly faster, by like a quarter of a second, and the charged shot won't make a player fall clumsily.

As it relates to swords and bombs, it used to have no chance, but the gunner version makes it a desired piece of equipment.

gunner Argent Peacemaker and gunner Sentenza:
Without using the original guns, since they're not available in the depot, they seem to fire faster, but I can't say for sure. Also the charge shot seems less likely to backfire since originally using it would allow enemies to get at you, but that doesn't seem to happen as often. Whatever's been upgraded with these, it won't damage the metagame by being overpowered compared to anything else.

gunner Biohazard and gunner Neutralizer:
Keep all the changes. Do not not release this. I want them badly now.

That's all I got. I'm not an expert in this area of the game, but in general I like what I see. This would definitely get more people to use guns.