For the Hatters who dont believe im gonna post this up again.
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Iruka is giving a lesson to the academy ninja about the previous kages. Hiruzen shows up and iruka says "just in time". The he introudces hiruzen as the third face on the mountain and says that he is the strongest them of all. Which refers to them all on the mountain, because the lesson that day was on the hokage.
Now hiruzens hype says that "IN HIAS PRIME HE WAS THE STONGEST SHINOBI ION HISTORY". This refers to shinobi during his prime and before his prime.
There are ninja that came after his prime that may be stronger than him. I.E Naruto, Kabuto, Edo Madara, Obito
But any shinobi that came before his has been said to not be on his level, DURING HIS PRIME. The problem with most of you is that you are trying to compair a old hiruzen to hiruzen in his prime. They might as well be two diffrent shinobi because even enma stated that there is a huge gap between thier power levels and abilities.