Yeah, I'm fine with homeworlds being well defended. I'm also fine with 400 Mu colonies being well defended. It's just that it's too easy to get to 400mu and on the way up they're orders of magnitude too difficult to deal with. Maybe colonies should require terraforming to get up to their current strength, but homeworlds can start off at that level? I don't know. A new colony should be barely hanging on though, not immediately become an impenetrable fortress until you're two weeks into the game :-)