I know and they can't be. But the AI sends lots of small fleets everywhere with those torpedo ships and that's just horrible.
Starbases shouldn't fall victim to small fleets, period. Large fleets? Fine! Small fleets? Terrible.
The only thing you can do with additonal upgrades, is to upgrade a few hangar bays to build bombers. That does not influence any big battle. It only serves to destroy a small fleet, nothing more.
Late game, when the AI has 2000 ships, the Starbase + defenses are COMPLETELY and UTTERLY useless for any form of defense anywhere on the map against almost any sized fleet. The AI sends 5 torpedo ships and a few escort ships? It's GONE ! Your whole defense is GONE.
Note: I was playing TEC.
Note to self: or I could play Vasari like everyone else.
Note to self 2: or I could place some ships there for extra support.
Well actually I was losing the battle quite badly and I was a bit upset that my last hope, the twin starbases, were obliterated like paper toys by this tiny fleet while I had to send the remnants of my fleet to the main battle, which I also lost. The starbase there didn't make a difference either.
Anyway I don't understand your complaints about this really. Starbase upgrades are really very expensive, and if such research is also expensive than it will hardly affect online multiplayer games, where defenses make little difference anyway because the players stay far away from them (they only work against stupid AIs, they act like a magnet to the AI ships).