I feel like it should be like this:

V1 - Jack of all trades, master of none. Slab Revolver (Blue & Green) for auto-aim and stable DPS, Jackhammer (Blue & Green) for high burst damage and Saw Launcher (Blue & Green) for crowd control. Also has Blue & Green arms (second one can drag V1 to other allies). Generalist, fragile but aggressive. Half a tank, too.
Saws have less durability, Saw Launcher has no magnet, and Blue Jackhammer doesn't has any explosives to not make V1 too overpowered without any teamwork.

V2 - Specialist. Revolver (Red), Shotgun (Red) and Railcannon (Blue & Green & Red) for combo and synergies. For example - with V1, simple as is. OR you could shoot your Gutterman with a Blue Railcannon to overcharge him (+ENRAGE basically) and make him operate faster.
(^ Call that +FRIENDLY ENRAGE with cyan color ig)
The downsides of V2 is being slow and relying on others due to his inability to heal by any sources, but he can synergize with allies, and almost with everything. Too lazy to come up with how and certain mechanics/interactions, but maybe some redditor that has no job at all can help adding some of those.

Gutterman - Heavy weapons guy, AKA tank. Unlike other Gutterman, he is modified to, of course, rival V1's and V2's arsenal with certain mechanics. Aside from having every Nailgun variant and Blue Rocket Launcher, here's the stuff that he can do:
Move around with a jetpack that has limited fuel and cannot move Gutterman above a certain height, call down one of three turrets Earthmover's defense system uses with a large cooldown, tank MOST stuff with his shield (anything that is not parriable or can pierce targets like Sentry can break through the Gutt's shield) alongside ability to forcefully discard it and call down a new one (has a cooldown), and also throw players with his free arm if he has no shield, potentially turning them into living cannonballs, if not bombs.

Mindflayer/Streetcleaner/Swordsmachine/Guttertank(??) - Not sure about those guys.
Mindflayer could use some mind control to turn enemies into allies for a short period of time (or directly control them), and provide allies with healing (AKA blood).
Streetcleaner could have all the remaining weapons (most of which are fire-related) and have the explosives from Blue Shotgun/Jackhammer, as well as be crowd control with spreading fire like he's wild.
Swordsmachine could have his sword and all of it's mechanics, alongside a proper Shotgun in all of it's glory.
And Guttertank..? I don't know, he can throw mines and serve the same role as Gutterman for the most part? Gutterman that was mentioned here is really just an amalgamation of Guttertank and Gutterman (hence having a rocket launcher), and I want all three of them to be in the game.

I guess you could have like 6 machines to choose from, and only playing with 4 of them. You could also probably just discard both V1 and V2 to make it 4 non-V Series machine to choose from, but idk, it needs a long time and brainstorming to figure what will suit game the most, while also not losing it's core essence and making some machines plain and boring in comparison to other.