First off, Where do you think the legend of hashirama's strength came from?. People in his Era? People that wittness the aftermath of his power? People that fought beside him or against him in the Senju vs uchiha war?
Iv'e already shown a very rough timeline for Hiruzen's hokage Reign, His Titles of God and strongest kage only came along a decade (give or take a fe years) after tobirama died which was mere years after hashirama died. People who started such legends, Fought along side him or against him (on the uchiha side) or even witnessed the aftermath of his battle with madara first hand. Unless they all died out in the 20years hiruzen was hokage or the 10 or so years he gained such hype a number of them were alive during hiruzen gaining such praise.
Hiruzen was only comparable to the other kage during his old and weakened state, Even then he was considered to be the strongest of the lot.
During his younger days it's pretty clear that no kage nor shinobi could compare due to him being hailed as a God of shinobi compared to other shinobi at the time. which included extremely powerful shinobi like, 3rd raikage, Hanzo, 3rd kazekage (hailed as the strongest kazekage), Young Onoki and such.
If hiruzen's strength was so believable, He wouldn't of been dubbed the god of his Era now would he.
if i have reason or not, Doesn't make my points any less valid.