1) In general, boarders move and fight their way through an enemy ship WAY too fast. I doubt I can even zoom in to watch in the time it takes them to slaughter my crew and take over my ship.
BUT what I really want to talk about is:
2) I think the game would be better if the boarder types had clearly differentiated personalities:
This needn't be too complex for example, using speed/movement when attacking through an enemy ship:
Crew doing boarding (currently not allowed i think?) = 1/4 speed
Arachnids (dumb name) = seem relatively weak, so maybe fast & aggressive troops = normal speed
Marines = 1/2 speed, very methodical but harder to kill and/or but enemies killed stay dead (can't be healed)
Grenadiers = 3/4 speed
Spiders (seem too strong) maybe their speed should drop from normal to 3/4 to zero (inoperative, spring has wound down)
3) Just had an idea, maybe a spider trap module, a hole in the deck which 50% of spiders will fall through.
You ever heard of guards?
Spiders and boarders are ridiculous, and guards are only a mediocre counter. A dedicated boarding fleet will stomp even a large number of guards. Reducing speed would be a decent counter but we really need a weapon that specifically targets enemy crew/soldiers when exposed on the ground or on top of a ship. Otherwise boarders will remain the strongest weapon in the game as they are a weapon with little to no counter.