How balanced would having a War magic ability ( similar to an eldritch knight) be compared to the extra attack on armorer at the fifth level

For roleplay, purposes imagine using thorn whip ( like a grappling hook- Boba Fett) then using thunder gauntlets ( like a Vibro blade), instead of 2 basic thunder gauntlet attacks

Or using a flamethrower ( firebolt) and combo it up with a revolver attack ( lightning launcher) or something

definitely will spice up the subclass a bit

Cantrips are generally balanced around being the one offensive action taken in a turn.  Anything else is a special class feature, or an option that takes specific resources a'la Quickened Spell or the like.  Especially for Lightning Launcher/Infiltrator builds, being able to replace their less-than-useful second attack with a much more powerful cantrip would be a big upgrade.

Game-breaking?  Likely not really, no.  But a definite upgrade to their capabilities, especially for infiltrators with nothing useful to do with most of their bonus actions.

yup, I think that would be a cool change, but I feel that would leave guardian pretty stale with a " double gauntlet attack"

maybe it would let you cast the cantrips at lower levels to where it has the same damage ( or lower) but with different effects, such as shocking grasp or thorn whip

I'd honestly rather than the attacks and extra attack, they give something that adds int mod to spell damage in some way. 

 @wegrata Are you referring to the thunder gauntlets and lightning cannon?

I feel redundant but after looking at the player's handbook

Page 193 under making an attack says and I quote: Whether you’re striking with a melee weapon, firing with a ranged weapon, or making an attack roll as part of a spell, an attack has a simple structure.

Which means all classes can do cantrips that "use attack rolls" as the attack action, for example, firebolt, shocking grasp, and thorn whip

Yeah I'd just drop that and extra attack, and give a bonus to spells that require an attack roll or something like that, just to set it apart from draconic sorcerers and some clerics. 

How is this subclass similar to draconic sorcerers? Clerics?

Forgive me, I am not familiar with those 2 classes specifically 

They both get spell stat modifier to spelldspell  just in different ways. Draconic sorcerer gets it to all spells based on element and scale color, some clerics get it to cantrips. I'm saying this should get it to spells that require an attack roll. So it could do shocking grasp with int mod to hit and damage. 

Quote from bigexplosion >>

I feel redundant but after looking at the player's handbook

 

Page 193 under making an attack says and I quote: Whether you’re striking with a melee weapon, firing with a ranged weapon, or making an attack roll as part of a spell, an attack has a simple structure.

 

Which means all classes can do cantrips that "use attack rolls" as the attack action, for example, firebolt, shocking grasp, and thorn whip

That is definitely not true. Spells require the Cast a Spell action, which may involve making an attack but is not the Attack action and doesn’t work with features like Extra Attack and Two Weapon Fighting. Such features use wording like “When you take the Attack action,” not “When you make an attack...” They’re different things.

@SagaTympana 

Ok, very interesting, what would you propose is done with the subclass abilities ( I feel like its very balanced already minus the helm of awareness infusion)

There is nothing wrong with hitting twice with thunder gauntlet or lightning launcher, but I thought maybe a combo ability would be pretty cool

What if the subclass did like "minor war magic" where it only lets you cast the cantrips at their lowest power level?

Are you looking to replace the Armorer's Extra Attack?  Or are you looking to augment it?

If you want to replace Extra Attack completely, then just give it War Magic.  The extra damage from the cantrip is at least partially balanced out by the fact that you get no second strike if you use the Guardian armor's temp HP bonus action.  The Infiltrator gets to do a ton of damage - 2d6+Int lightning damage on top of whatever your (Firebolt) cantrip of choice is - but eh.  If your table likes punchy shit like that, who cares.

If you're looking to do both - get Extra Attack and War Magic, attack twice with a weapon and once with a cantrip in a turn - I would suggest putting a limit on the number of times you can use the bonus action.  Intelligence modifier or Proficiency modifier.  This is honestly the more powerful option, even if it's limited in use, as that's a lot of damage to be chunking out there without a single spell slot or other consumable resource (other than its own ammo) being used.

I am looking maybe as a potential option to do either or, maybe you can choose to do a second attack on a second enemy to taunt both or choose to use thorn whip and the gauntlet on the same enemy ( but not doing 2 attacks and 1 cantrip, just 1 cantrip and 1 attack). That way you can do different combos depending on the party composition since thorn whip and shocking grasp have secondary effects reinforcing armorers role as a support/tank character

You could also do those combos by taking those cantrips and simply forfeiting your attacks for the turn.  If your DM is running the game close to the book and not adjusting encounters for higher-powered PCs, that's your option.  Attack or cantrip.