Arty has the advantage that can quickly regain his air strikes at the price of having less coverage than Skyhammer, they are more controlled than Sky, but less so than Kira who has absolute control over her laser. His ammo packs make him a good source of quick ammo supplies if the player is reliable especially when he can shave off precious seconds like Skyhammer with direct hits, unlike Kira. His artillery id best used in a mindset of " if I were on the enemy team where would I be coming from", along with best used looking at the map’s walls and surfaces for unexpected strikes.
The unreleased fire support Stoker is best seen as a mini Kira/Sky oh Sky’s side he tosses his explosive (Molotov Cocktail like incendiary grenade) and works great in doors with 2 automatic rifles and 1 burster, while on Kira’s side he has an ammo station and area denial as his priority, also still as effective indoors as he is outdoors, something Arty and Kira can’t do and Skyhammer can at the price of low damage.
As for the Nader/Fragger thing I’ll bring in Rhino aswell.
Fragger fills a middle ground so to speak with quality over quantity, 2 powerful grenades that can be cooked for close range damage and an LMG/Rifles for good close/mid-range damage dealing.
Rhino is great at close range damage dealing with his minigun but lacks grenades for damaging enemies around corners and indirect fire, and his shotgun lets him have the reach his minigun lacks, his higher health makes him shrug off more than others but lacks speed, making him best used indoors where he can’t be sniped and near a medic, hopefully a healing station.
Nader has quantity when it comes to grenades, excelling at indirect fire and long range damage dealing but has an SMG for when her grenades can’t detonate fast enough due to the range and lacks health making her squishier and expected to be more on the move.
Edit: If you dropped 2 artillery strikes as Arty on a full health EV you’d be doing around as much damage as one Skyhammer Air strikes, but the lack of as much damage I somewhat believe is acceptable due to its range and better control.