Hiruzen is confirmed to be one of the best ninja the Leaf has ever produced. To say- no, to even think that Hiruzen wasn't utilized in these wars which I presume the goal is to win is completely and totally laughable.

Naruto is even stronger than hiruzen, yet he's not sent to most combat based missions cuz he's to busy managing the paper work. For some reason kishimoto doesn't understand the difference between a political leader and a powerful warrior, a leader is gonna do diplomatic shit and manage the village, mostly desk jobs that will absolutely ruin a great warrior. But there is work in managing the village during times of war as well, the leader cannot abandon that role and go fight on the front lines, no matter how powerful they are. The kage did fight in the fourth war but that's mostly because all the villages were fighting against a common enemy, so there weren't many diplomatic responsibilities left, and even then the hokage and raikage were at hq till madar showed up and played a relatively small role in the war.