Honestly ,there isn't anything too misleading about how Garmin markets their products. Maybe a little confusing but not misleading. I would venture a guess that you purchased the system yourself & bypassed a dealer. Not that there is anything wrong with that, IF you know exactly what you need & are able to spec out something as sophisticated as an autopilot system without the assistance of a dealer or certified installer. I would also guess that the reason that the dealer who sold you the system wont take the corepack back because you had installed it before you realized you ordered the incorrect one & now it's a used part.
If my assumptions are correct, there's really no reason to be upset with their product or company..