taking rage spec as an example, i think marauders can last longer due to their utility... juggs cant do much if they get jumped and they dont have any escaping ability... marauders can also smash faster , therefore more damage.
i have a juggernaut and a marauder and if someone thinks what i said is not right then by all means explain, im giving up on my smash jugg because i die too fast. full partisan gear and half of it is augmented.