During obito's attack on konoha hiruzen pretty much single handedly pushed the 9 tails out of konoha while minato 1v1'd nobito. Took over as Hokage while he was Naruto's age in pt.2 and managed to remain the hokage the longest out of all the other hokage who dead prematurely, "God of Shinobi", pretty much raised naruto, Hiruzen beat the edo tensie of the 1st and 2nd and after wards defeated orochimaru.
Let me elaborate:
Hiruzen is faster than Tsunade although she is stronger.
Hiruzen has more chakra reserve and ALOT more jutsu than Tsunade who we havent seen use 1 jutsu to date
Hiruzen has King Emma, Tsunade has slugs that arent offensive
The ONLY way people can even say she comes close to beating Hiruzen is because this say she has Byakuya < ik i spelled it wrong, while missunderstanding what the ability does. Her fight with Orochimaru points out the fatal flaw of it which is that she still needs to breathe, any poisening or smoke clouds and just suffocating her would take her out, this added to the fact that she has no long distance jutsu but is strickly a taijutsu brawler means that she will be at a huge disadvantage since getting into range to attack means getting into range to be poisened, etc...
Secondly people are comparing Hiruzen at AGE FREAKING 70 TO TSUNADE?? REALLY SHE IS HALF HIS AGE, Im surprised Hiruzen could even walk and yet he is taking on 2 edo's and oro at the same time AND WINNING??? Let me end it with this, Hiruzen in his prime was the strongest hokage ever, meaning he was stronger than hashirama, madara already showed tsunade was no where near as strong as hashirama by the fact that her + 4 other kages couldnt even make him sweat.
Come on people.... Lets be serious, barely and I mean BARELY beat orochimaru when he had no arms and it was her and jiraiya and naruto vs him and kabuto, Hiruzen took on Orochimaru with jutsu and 2 other edos and still managed to win, the only reason orochimaru survived was because hiruzen didnt want to kill his own student.