Firstly: culture
Culture is fairly subtle, and it's not meant as a brute force way to gain planets. Basically, Culture has these effects:
- It raises yours (or your allies') planet allegiance by 10% on any planet it affects. This means 10% extra income from the population and ore/crystal mines.
- It reduces enemy planet allegiance on planets it affects. This is harder to do because the enemy can combat with his own culture, but it's the backwards effect. His planets make less money, and if you manage to get a planet to 0% allegiance, it will rebel and turn neutral. This obviously starts taking long times the closer the planet is to the enemy's homeworld, but for vast empires with far reaching borders, the planets on the outskirts can only have 35% max allegiance (discounting an Advent tech).
- Each race gets a bonus in friendly culture. TEC have higher antimatter regen, Vasari get a damage bonus, and Advent get a shield mitigation bonus. This is added on with the culture research line, doesn't happen by default.
The Deliverance Engine shoots a massive amount of your culture anywhere - can be your planet or your enemy's. Because allegiance gain/loss has a cap, you would need to chain several shots of the Engine for your culture to last long enough to drop a planet to 0 allegiance, because the culture from the cannon decays. And, since you can shoot it at enemy planets, that means when you're fighting at one you can take away the enemy's culture bonus (really sucks for the Vasari), and you gain yours (yay!).
In essense, Culture is more of a support mechanic than a direct combat one. It's highly useful, and if you ignore it you can lose all your planets to it, but culture tug of wars take a while to "win".
Another thing that I wonder about: fighters or bombers?
Fighters do incredible damage to long range frigates, siege frigates, and of course other fighters/bombers. Bombers do great damage to capitals, heavy cruisers, and structures, and "okay" damage to everything else, but a fighter squad will do quite a bit more against those LRFs and siege ships than bombers will.
In short, they're definitely very useful. The rule of thumb is adapt to your enemy, since you can change squads around on the fly. If you have to blast through some sticky defenses, or lots of heavy cruisers, bombers are the way to go. If your enemy likes massing LRFs or tries to siege raid, go for fighters.
