1a. Not really. Bombs are the kings of handling massive mobs. For example, in FSC you have powerhouses like the Nitronome which does normal damage but can easily hit over a dozen targets, the DBB which pretty much does the same thing as Nitro but with lower knockback, the RSS which can be used as a makeshift grenade, the Electron Vortex which sucks a large group into one point, and the Voltaic Tempest which has massive dps in large crowds. Not to say guns are bad, but they're not designed for crowd control.

1b. They're pretty much equal. Alchemer charges and Antigua rapid fire can do just as well as bombs when facing small clusters of enemies.

1c. Yes. Bombs generally rely on area-of-effect attacks to achieve high dps, whereas with a gun you can simply unload the clip into one enemy and kill it in a few seconds.

2. No. When you're soloing, the low health of enemies means that one of bombs' main weaknesses (general lack of adequate single-target dps) doesn't matter much. Also, as a solo bomber you can spam the Nitronome all you want, since every combination of bomber armor and trinkets will give your bombs maximum CTR. However in a team, guns are better since their attacks don't interfere with your teammates, and you can teamwork with guns (for example, combining fire on a target, or using your guns to aggro turrets, or providing suppression fire to allow teammates to get out of sticky situations). The only support bombs are the Vortexes and Vaporizers, neither of which a bomber is going to be using very frequently compared to damage bombs.

3. Potentially yes, but it'd be difficult. In FSC I mainly use a Combuster [UV: CTR low] with Skolver Cap, Vog Cub Coat, Barbarous Thorn Shield, one Elite Sword Focus Module, and one Elite Quick Strike Module, which grants the sword DMG very high, ASI very high, and CTR ultra--I don't see a gun easily outdamaging that thing.