The 5th Hokage is the weakest. You have to look at combat ability. Mei could kill a whole battalion with just her acidic mist that melted even susanoo. Then theres her lava style which is far hotter then any normal fire(It takes super high heat to melt rock). Plus she can use water, fire, and earth jutsu as well. Garaa can control sand and as seen he can create sand from the earth below him. Majority of his attacks crush using virbrations to compress the sand. He may not have one tails but his abilities combat wise attack as both a weapon and a shield all at once and he may have been defeated by Deidara but he also had to protect his village at the same time. Oonoki is probably the most impressive because he has a bloodline expansion. That dust style looks like its a fearsome jutsu and the recent showing seems to back it up along with his uber jutsu making his comrade scared he would destroy the island if he used it to close to it He can also use wind, earth, and water styles. Raikage is probably the fastest out of all the kage and his sheer power is tailed beast level. His taijutsu have added lighting style for increased speed and power. Plus he is protected by lighting armor. As of yet we don't know what those spiral tattoo's mean on his shoulders(taking this idea on how Darui's tattoo's mean something). Now Tsunade as we've seen only uses hard hitting taijutsu in combat. She did use that one jutsu that messed up Kabuto's nerves but she got beat by someone who is only at Kakashi's level. She uses uber medical jutsu but compared to Kabuto pre-Oro implant she was nothing and got saved by Naruto a genin. her punches are only god if they hit and she has no real speed and didn't even use chakra medical blades in combat like Kabuto did. She is only praised for her medical abilities not her ninjutsu. Of the three Sannin she is by far the weakest and the weakest of all the Kages. If you look at the previous Hokages she is also still the weakest. Shodaime beat Madara and was known as the strongest man of his era. Nidaime created edo tensei, created the blue print for space time jutsu, and used high level water jutsu without water. Sandaime was known as the strongest of the current kage at his prime and was nicknamed the professor for mastering ever jutsu in the leaf village. Yondaime was so feared there was a flee on sight order for entire ninja battalions(during Kakashi's Gaiden he took out a battalion using flying thunder god), and was known as the greatest shinobi that ever lived(no one believes rikudo was a real person). Even Danzo for his breif stay as Hokage was better combat wise then she is. The rare wind style, plus Izanagi. All the other Kages of the past were equally feared and only killed by a Kage or Kage level ninja. Tsunade was beat by a Jonin level ninja and barely beat a no armed9sealed armed) Orochimaru. If Oro had his jutsu Tsunade would have been beaten a long time ago. Don't get me wrong I don't hate her but combat force wise she is not stronger then any other kage with just her taijutsu. Kabuto used a mix of medical and taijutsu and even Tsunade says he is better then she was in her prime(see episode).