Hiruzen Sarutobi is the Third Hokage of the Leaf and while he can definitely fight at a high level; he will always be in the shadow of Hashirama. Hashirama was the original Hokage and many still consider him to be the strongest one of all time. His hand to hand skills are light years ahead of Hiruzen Sarutobi’s and Hashirama is also a great deal faster. Hashirama wins.
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Because all characters are at their best, Hiruzen gets to fight as though he is much younger, yes?
Yes, although it won’t help him a great deal since we only briefly saw him in his prime during flashbacks and such. It would ever so slightly help his speed, but that’s about it.