The shipping is deplorable. There is NO excuse for that sort of shipping. No insulation means that heat pack was useless and no padding means the snakes were tossed around inside. And he's wrong, the "live shipments" do go cargo as far as I'm aware. That's why we always use the special shipping packaging so that they are protected during the trip.
That said, you should be able to insist on a full refund and you return the snakes. Asking for a partial refund where you keep the snakes is less correct. I know he said at one point you could return them for a refund but said you'd pay the return shipping. Since the animals are not as advertised, he should pay return shipping as well.
He definitely is trying to screw you over. I would discount the broken ribs, since snake ribs are easy to break and no way to tell if that happened before or during shipping. The RI, the WAY off weights on at least two and the lousy(possibly illegal) shipping is grounds for a full refund BUT, you'd return the snakes.
Someone should also contact SYR, since he apparently shipped using them but shipped ignoring ALL the information about how to ship properly. They might ban him from using their service in the future.