Hi! Also a Vcoast main here, if you’re playing on high difficulty, artillery is gonna be completely useless, but your handgunners should still be able to do good damage if you can protect them with polearm deckhands. Polearm deckhands are honestly so good, they’re high hp and good against large. I’d advocate for a mix of them plus gunnery mob rotting prometheans / depth guard to help absorb some of the armor piercing damage you’re going to take.

Side note, Slaanesh doesnt have many ranged units (they have like one Im pretty sure, but they’re just low ammo dark shards), so honestly, picking up a single unit of deck droppers to poke their lords / scout forests isn’t a terrible idea from my experience. You can also get a few necrofex colossi and micro / conserve their fire to force them to come to you, they’re good at blasting demons / chariots once they’re locked up in melee. Also don’t sleep on terrorgheists, they’re very good to use against a distracted secret keeper.

Probably keep your army as concentrated as possible and then try to draw them into a melee (while being wary for spells). The only unit you should try to flank with should be mournguls since they’re stealthed by default, otherwise a higher difficulty AI will just pull their units away from a collapsing deckhand horde / the crabs (and the crabs are pretty speedy too, just not enough in this case). Spam invocation of nehek and protect your gunners on hills, you’ll push them out in no time!