People need to keep in mind that we are still in the beta release. This is NOT the final version of 4.86, and you build player bases at your own peril and must be willing to accept the consequences of losing a base that still has bugs and imbalances. If people want to improve bases, you guys need to put together some well-worded posts on how the improve the system, and post it in the development section of the forum. Keep those posts objective, and try to keep bias out of it. A base possible to keep invulnerable isn't a way to improve the system, that'd only make it worse (OC base above Crete for example).
There is already a base balance thread created by Cannon for these issues in fact. The idea that one should need the firepower of a battleship or a large force of smaller ships sounds like a very good one to me. I personally would like to see a system where the shield recharge is the main defense, and the attackers will need a large force able to put out enough damage to counter the shield recharge and still drain it. Shield recharge would equal something like 50% of the DPS a BS can put out. That means BSs would be valuable in base killing, but that smaller ships in groups can also still do it. Even with a BS, it should take 2-3 hours to drop it, and then when dropped, it should go into another mode that makes it invulnerable, but also undockable, for something like 12-36 hours. EVE has a very good POS system set up and we could take many tricks from their setup to improve ours. Bases going into "reinforced" mode after teh shield being dropped or taken into a very low percentage would be good, as it allows the defenders to have time to organize a defense of the station, and when it comes out of reinforced mode, they simply have to defend it long enough for the shield to recharge.
That means you'd need a total of about 5-6 hours of attacking a base, half at the start, and the other half a day or two later. Less if you have a LOT of firepower.
A lone bomber should have no chance of dropping a station.