you know, the funny thing about all prime hiruzen hype ever, is that it can be refuted with the same 2 panels that "prove" it.Nowhere did the manga state that Naruto became the strongest Hokage. Unless that was stated directly, Prime Hiruzen is the strongest by default since that is what both the manga and databook states.
"The third was said to be the strongest of all"
WAS. implying that someone came along and was stronger than prime hiruzen. and given that hiruzen retired and gave the job to Minato, a guy who soloed an entire war, i have a fairly good idea who. then there where the other insanely tough guys who came later who would beat prime hiruzen by blinking too hard.