Thats without Tsunade's say and Kakashi is in a way alot like Jiraya. Unless if he has no choice he rather not take the burden. He was pretty relieved when Tsunade recovered after Pain's attack. Hokage is given to the village's strongest if I remember correctly. All the hokages before Tsunade were the strongest in their time. Jiraya was the strongest and was chosen to be Hokage but he pushed it on to Tsunade. Possibly he did the same when the 4th died with the same undercover work excuse. As of right now Naruto is the strongest in the village. Only thing working against him is his age and the elders not to fond of Naruto but Tsunade doesn't give a damn.