Well, Allegiance, I do agree that starbases on stars are certainly not overpowered, but all the same, when on your planets, a properly supported SB can take on quite a bit before succumbing to the invaders. Take the first Orky I ever built. With only two repair platforms, a PMT, and a hangar to help it, it still managed to fend off four good sized fleets. Sure, they weren't monstrous, but they were of a decent size nonetheless. It also managed to slay around 40 Orgovs. The Orky never actually died, as combat eventually moved elsewhere and the AI stopped wasting resources against my beloved Orky that quite possibly won me the game by preventing the AI from flanking my main force before I had phase gates up and running.
So, my point is that Starbases can be powerful roadblocks if supported correctly, or if on a star, are mere speed bumps... Now, of course, four fully upgraded Orkies with every last upgrade done to them are pretty dang hard to punch through since unlike Argonevs you can't go around them easily... You have to go through them, and Orkies don't like visitors.. With each one potentially dealing 600 DPS you have 1800 DPS plus the 12000 Hull and 7500 Shields (plus the deflector shield which might I add is freaking awesome). If you use a mod such as Distant Stars or Mad Scientist, those phase missiles will more than likely go through your shields..
For instance, I had my Orky in a battle with a level 5 Kol today at a star. The Orky was fresh, so it didn't have much in the way of upgrades, so I began quickly researching Pulse Gun tech. 40% extra damage is a lot, and it definitely helped chew up the Kol. Eventually though, a level 6 Marza was brought in along with a small group of LRM's and Cobalts to aid the Kol. Then the phase missile upgrade kicked in, doubling the damage my Orky could put out. I then siezed the opportunity and quick-teched PM tech from the 20% I was at all the way up to 60% and then researched the damage to get it up to +40%. The result? Everything within range died. There were no survivors from such a powerful barrage of Phase Missiles.
That said, I don't think SB's are OP. They are powerful yes, and when you have technological superiority over the enemy when using a mod that amplifies the effects thereof, you end up with one thing slaying all that comes in range. Really the problem with this is the AI's inability to place them.. If it would, it would be much better off.. Four Orkies are a great roadblock. You can punch through them if you try hard enough, but most things will just get turned into their breakfast as they suck your ruins into their maws...