Brief Update:
I didn't give up on this game, I actually hammered at it for an hour or so last night. Gillman is proving to be a tough nut to crack (although I'm definitely making progress).
The AI was using its reserve to defend the planet, plus there is a parasite eye, and a lot of the guard posts are shielded and protected by a fortress. On top of this, the fortress has both a spider and a tractor 'thing' (don't remember they were guard posts or guardians, I often get both confused) defending it... there was also a ion cannon next to the fortress.
So basically I was fruitlessly throwing bomber strikes trying to dismantle this defensive monstrosity while the reserve units chewed me up from behind (and half of them got engine killed as well). I believe the guard post on the planet was also a special type that made the enemies faster (ugh!)
Somewhere in the middle of this assault, the cookie monster decided to slowly move back and forth along my reinforcement path, so I had to kinda wait him out. And my ball on Ocean Dragon waiting to reinforce would sometimes get harassed by the rocket silo on that same planet, cause you know.. it wan't easy enough.
At this point, I've managed to dismantle the annoying stuff around the fortress (but not the fortress itself), and I stopped being dumb about the reserve ships and simply popped the command station to stop them from spawning (once it clicked for me that it would do this). I was a bit hesitant to do this before because of the barracks, but those units being unleashed is not nearly as much of a pain as the reserve.