Although Hiruzen does not have enough feats, but I agree. He is stronger than Hashirama. Hashirama has never, and will never be the strongest Hokage, there is no single time in the manga that stated otherwise.
Fanboys always get butthurt or jump to conclusion that if they did not see something, it's not true. However, kishi proved again and again that the statements in part 1 are actually true! We just did not see Hiruzen in his prime, but that does not make Hashirama stronger than him!
Unless there is a direct statement that "Hashirama is the strongest Hokage" he will never be the strongest. It does not matter who deny that because simply that won't change what was stated in the manga.
That how I see it at least.
There is no statement saying "hiruzen is the strongest hokage"
The statement said " hiruzen was SAID to be the strongest hokage"
meaning it was what the characters in the manga thought, before saying just because its written its law you have to remember that people also didn't believe in hashirama's hype when they heard it they discarded it as fairy tale.
If these said characters discarded hashirama's hype but believed hiruzen it means hiruzen was on a lower level that is believable if you hear about it, people could accept it (don't get me wrong i am in no way saying hiruzen is weak ) he would make my top 10 if his prime existed ( but there is no proof of it yet so yea...)
hashirama >>>>>> old hiruzen by far
hashirama > prime hiruzen (considering hashirama would be at his prime)
now i understand this is probably a troll tread of some kind but my point of this is also that you can intepret what you want from the manga to come out with an answer supporting your character (with the manga i believe hashirama > hiruzen until they said otherwise by someone relevant or they show hiruzen prime who is so op it make hashirama look normal) i can give enough hype to match hiruzen hype by using the manga.
his professor can be matched by "The clan with a thousand skills" (the Senju were prodigious in all skills, from ninjutsu, to taijutsu, and genjutsu.)
the god of shinobi title they both have now
the strongest hokage ( debatable as i stated above)
strongest of their time which they should both have i guess