I wouldn't mind ground combat in starfarer if it were handled like boarding operations, it's just a matter of bringing enough marines and hoping for the best. Perhaps you could also have ground vehicles that work like marines only more powerful. They would take up cargo space instead of crew space. So if you wanted to invade a settled planet, you'd go out and buy a bunch of freighters and crew transports and recruit a few hundred marines and buy a couple dozen tanks to dump onto the planet. Then when you get to the planet, you select the "Invade" option, and it works out the winner.