Should a person log off - their hardpoints would need to be redistributed to the others.
At the moment - bombers succeed against caps by use of a 'wolfpack' strategy. Whilst the single player cap shoots at one ship (who flies defensively) the others pummel him.
So if a player logged off - sure there would be a disadvantage to the cap ship - just the same as any group of players would have a disadvantage if one of their team logged off during a furball.