To be fair, before the latter half of the war arc, there is more to who wins a fight than who has the highest destructive potential. 3rd Raikage couldn't even get a single hit on a clone of Naruto for all his speed and physical strength.
Hanzo especially would have a way to deal damage without worrying about that armor with poison. So I don't think it'd be as lopsided a showdown as you think.
Hanzo's poison may be strong...but I don't see that swaying the battle for him.
We'll attribute the three Sannin surviving Hanzo's poison to Tsunade, but that means that however briefly, it was possible for one of the Sannin to hold off Hanzo
and not get hit by poison while Tsunade was healing whoever was down.
For the Raikage who's speed and reaction should surpass and individual Sannin, I don't see him having major problems with the Poison.
This is assuming the poison is strong enough to actually take a Sannin out of commission in a relatively quick time. Otherwise, if they can fight
while the poison is coursing through their body, then Raikage probably kills Hanzo anyway because his poison isn't potent enough to quickly win him the fight.
Also...I don't see any of the three Sannin or Hanzo being as fast as a KCM clone :v
So we're not sure if they could dodge the third Raikage as Naruto could.
The best senses on the Sannin team likely belong to Sage Jiraiya, and Naruto as a Sage is cuts above that.