For 1: Hiruzen did not have to fight as much during his reign as hokage because he had powerful shinobi at his hand. This would have led to the dwindling of his skils in his old age. Unlike danzo who frequently went on secret missions long side orochimaru and his root agents.
For 2: The only reason danzo has a chance is because of KA and the sharingan. If not for those i think an old man who fought on equally with orochimaru the first and the second hokage is more than capable of beating a man who he beat out for hokage the first time around.
For 3: Danzo showed no real skills against sasuke besides the sharingans if had not had the sharingans sasuke would have easily defeated him. On the other hand despite the fight being trash sarutobi showed better skills than danzo
Last: is up to interpretation but if we go by hype
1. Sarutobi beat out Danzo for hokage
2. Sarutobi has 5 different chakra types and is aasumed to be proficient in them, hence the title "God of Shinobi"
3. Sautobi can be considered th grand master to the most powerful characters in the series. They include:
Jariya who trained Minato and Naruto, and i can throw in kakashi since minato trained him.
Orochimaru who trained sasuke
and even tsunade and sakura
All of who i believe could defeat danzo besides sakura(unless she used cry no jutsu