I think that the mech should be the response to player aggression. It should be powerful and scary, acting as a shield and juggernaut through the deepest most dangerous areas. Imagine escorting your crews submarine, patching it up with a repair tool that also doubles as a defensive weapon, and being flung around while wrangling alien predators, just like Marguerit Mada. Could also pry open giant hydraulic doors, make special repairs, stuff that makes it feel like dangerous heavy machinery