I completely agree with you. The third hokage let orochimaru go when he could have stopped him. The third hokage let the elders and danzou make wrong decisions. Tsunade never let the elders or danzou do what they wanted. It was thanks to the influence of yondaime minato that third war stopped. He wasn't able to find an alternative solution to the uchiha massacre in time. This is far too many failures for a hokage.
However, the hokage who made the worst mistake in naruto verse is the first hokage (harishima). He was so genius and said "let me share the tail demons to the other village so it can be balanced and treat them as tools". The good descendant of the sage of the six path treated the tail demons as tools. No wonder the tail demon started hating humans. The tail demons are ranked by their tails, there is no balance in that. One tail demon is weaker than two tail demon. If konoha was going to stay with the most powerful tail demon among the tail demons, how is this balance? Now that each village had a taste of having the power of the tail demons in their power, they wanted more tail demons in their possession. Most of the ninja wars were attempts of taking control of the tail demons. Rather than creating balance, he caused chaos.