There's people who lived through both Hashirama AND Hiruzen's primes. Yet who was called the strongest Hokage, "The God of Shinobi," and "The Professor?" Those people wouldn't just go like "oh yeah what we saw of Hashirama wasn't real; it was just a myth!!! Hiruzen is our second choice then!!" The fact is, those people who witnessed both of their eras considered Hiruzen better.
1. Here's a copy paste from one of my other posts:
"And yes, people from Hashirama's prime witnessed Hiruzen's prime. Say there was a 20 year old guy living through Hashirama's prime. Hashirama died not too long after his fight with Madara (5 years at max), because Tobirama looked the exact same as Hokage. And Tobirama stayed the same looks-wise when Hiruzen became Hokage. I'll be generous and say there was a 15 year time gap in Hashirama's death (at a young age) and Hiruzen becoming Hokage. 10 years later, Hiruzen probably reached his prime. That'd make the 20 year olds from Hashirama's era around 45-50. So I see no reason for them to have witnessed Hiruzen's prime. Hell, add in another 10 years and they'd still be able to witness his prime. Forget it, add another 10 years on top of that and they'd still witness it. And who was called "The God of Shinobi" or "The Professor" by them?"
2. Possible explanation for Hashirama being considered a myth:
And did you guys ever consider that Hashirama's power was possibly called a myth because he was the only user of Mokuton? Or maybe myth meant that Hashirama's techs were on a much larger scale, size-wise. That doesn't mean anything in being the best Hokage. Being a myth doesn't automatically make you above everyone else.
3. And here's a little more proof, regarding Orochimaru and his Edos, for those yet-remaining skeptics:
Orochimaru PERFECTED Edo Tensei, meaning that he had prime Hashirama as one of his pawns. It just didn't seem like it because Part 2 power scaling > Part 1 power scaling (Tobirama's basic Suiton was considered Kage level). Anyways, Orochimaru still considered Hiruzen as the strongest Hokage, and "The God of Shinobi." Did you notice that he was only taunting Hiruzen's old age, not his actual ability compared to Hashirama and Tobirama? And note that Orochimaru despised Hiruzen, yet still complemented him as someone who used to be the strongest Hokage.
So in conclusion, people who saw both of their primes still considered Hiruzen the best Hokage. Case closed.