the fight with tsunade and jiraiya, dont forget tsunade was already week(she fought Kabuto) and jiraiya was on drugs(made by tsunade) all three were handicap so it wasn't a full out fight.
itachi was stronger than oro, he(oro) said him self that's why he couldn't take his body.
jiraiya was stronger than itachi and kisame combine, they didn't want to fight him when they were looking for naruto, because it would be too dangerous
i understand one thing, when the manga began oro was shown like the ultimated bad guy
so i can understand why it sucks a little bit the way he died.