Hanzo according to hype was one of the strongest Ninja in his Prime. Hanzo defeated all 3 Sannin w/ seemingly ease. People often bring up the fact that Sannin were weaker back then to down play this; i'm sure they were weaker, but nothing indicates they were weaklings; after all right after fighting Hanzo they became extremely famous for their strength. So they must have been very powerful as a single unit even back then. Also to put additional context on this, due to Jiraiya's experience against Hanzo back then, he concluded that it was impossible any living shinobi defeated Hanzo. This is despite the fact that Jiraiya was aware of Shinobi like Orochimaru, other powerful Akatsuki members, and of course himself; so he clearly considered Hanzo stronger than these shinobi. Than we have Nagato saying the reason Hanzo lost to Pain Rikudo was because he had become rusty clearly implying Hanzo in his prime would have had a chance to win.
People underrate Hanzo because of his performance as an Edo Tensei, but he was the single most handicapped Tensei in the war. Not only was he given the handicap of being rusty by the author, which is significant; Rusty Tsunade for instance was losing out to Part I Kabuto; however he also he was also handicapped in the sense that he went up against the one guy in the war that was immune to his poison. And now we find out all Tensei are weakened somewhat from their living form on-top of that.
Regardless of these handicaps Hanzo still managed to clash evenly against the strongest Samurai for over 5mins and then ultimately killed himself off by defying Edo Tensei commands; being the only Tensei to do that w/o outside assistence besides Hashirama.
Him running from Nagato is also another thing people use to downgrade him, but Nagato was a Rinnegan user whose abilities place him among the strongest in the Manga cannon, additionally one must consider that the hype of Rinnegan out stripped even Nagato's own power at the time and Hanzo probably had already begun his decline into becoming Rusty, as he clearly had already started resorting to tricks and underhanded tactics instead of taking to the battlefield directly himself.
So yeah Prime Hanzo by hype should at least be around Pain Rikudo's level, possibly even stronger. Now whether someone believes the hype or not is up to them; but Kishi consistently keeps hyping Prime Hanzo and provided a great deal of excuses for Hanzo to underperform to that hype. Granted him even his rusty state some of the most hax'd abilities in the manga cannon, such as Poison Breath, Poison Cloud, and the the physical ability to clash evenly w/ Master Samurai for over 5min despite being rusty and only requiring a scratch to win. So Kishi has not really hasn't given me a reason personally to doubt Prime Hanzo's strength
