Hanzo was pretty weak, thats why he felt the need to take Konan hostage and force Nagato to kill Yahikio, thats why he retreated the moment Nagato started to fight back.
He just happened to never run into a strong opponent until Nagato, not very hard since his country was devasted by war and most of the strong ninjas were probably already dead. He probably hid in his castle until the very end of the war. The 3 Sannins were kids back then, alot weaker than now/the moment they died.
Nah no respect for Hanzo, he was a coward. Hiding behind his army and running away the moment he met a strong opponent.
Look at Jiraiya, he knew that he didn't have a chance in beating the 6 Paths but he still decided to fight till the end.