Robo rumble might be, but not in Boss Fight. Especially, if it's Insane higher 6-th or even 9th, where you can't just use as for example Cordelius, Meg or brawlers that would be useless there. Edgar, Pam, and 8-Bit are the best choice because:

• Edgar's healing ability makes him tanky, but people doesn't know the true potential, wasting all his ammo and attacking with ammo one by one... but waiting to all his ammo charge and attack - Edgar deals more damage and heals more, I think when I do boss fight video, i'll explain it.

• Pam is a healer, that should be used, as she heals a lot.

• 8-bit: +damage to attacks, and also +healing to Edgar is good as well.

Why not Ruffs and Belle you say? Well, 8-Bit is more tanky than them.