I wasn't aware that Kakashi is comparable to the Sannin. Is that the general impression? I note that in the edited canon, he's the one who was injured and told to retreat before the Akatsuki even showed up, for whatever that's worth.
I note that of the two Akatsuki that Jiraiya fought, he only identifies one as S-Rank. He did specifically note that there were a bunch of chuunin amongst the Akatsuki forces--it is possible that his second opponent was only a chuunin.
However, the overall strength of Akatsuki must be judged by their numbers and levels of S-rankers, not chuunin. It doesn't mean anything that Jiraiya and other jonin and S-rankers can kill chuunin if the S-rank Akatsukis then step in and stomp them.
I agree that Akatsuki was being smart, and that makes them more terrifying, not less. Bottom line, Leaf is now down the God of Shinobi, the Nine-Tail jinchuuriki, and a whole bunch of Anbu. Even if Jiraiya and a few others like him are as strong as the best Akatsuki's got one-for-one, it is probably that Akatsuki has the advantage.
But let's assume that an all-out Leaf assault could defeat Akatsuki. It's possible. Is that any reason not be smart? Putting Hazo on front-line duty is just a waste; he's chuunin-level at best, and will die very quickly when and if he ends up fighting an Akatsuki S-ranker. Maybe he'll get lucky and give the guy a scratch in return.
Put him on munchkining, and there's a chance he'll come up with something revolutionary and unexpected, something that allows Leaf to put Akatsuki down like a pack of rabid dogs.