Proof Hiruzen deserves top ten if not top 5
Hiruzen feats (Everything in the spoilers are manga pages to support my argument excluding one because I have no idea where that page is.
Konoha called him the professor for being able to use all the jutsu that existed in the leaf.
He truly expressed his mastery of ninjutsu in his entire fight with orochimaru. Lacking large chakra reserves yet holding off hashirama/tobirama and orochimaru is a feat within itself not to mention it means he had perfect chakra control since it was stated he did not have chakra reserves like he used too.
He fought against perfect Edo's. I will explain why they were perfect with proof from the manga.
1: Orochimaru did not show any concern of them lacking power. He was slightly impressed with tobirama's suiton skills.
2: Kabuto stated that orochimaru had perfected Edo Tensei later in part 2. He even went on to say that they could use all their original techniques which I believe was kishi subliminally implying that Hashirama and Tobirama were fighting at their full potential. Also to be noted is that Zabuza/Haku/3rd Raikage/Nagato ect did not show a decrease in power when fighting with no emotions. Even Naruto went on to say that he was more powerful after his emotions were gotten rid of.
Orochimaru had full knowledge of Hiruzen but still could not destroy the leaf village due to hiruzen sealing his ninjutsu and the 1st/2nd hokages.
Hiruzens chakra while severely lacking had a powerful aura to it. It was able to shatter the very ground he was standing on when released. In my opinion that's badass in every aspect of the word.
His speed with hand seals was incredible. Being able to match Orochimaru who was originally supposed to be hokage and being able to attack the 1st and 2nd hokage before they could even form a seal with Fire Dragon Napalm. Lets not forget Orochimaru was a prodigy and a genius ninja.
Hiruzen showed absolutely no fear when the thought of facing the 1st and 2nd hokage's went into his mind. His only concern was against Minato. This shows that Hiruzen while already confident about beating orochimaru was confident in beating the 1st and 2nd hokage as well.
He was able to destroy Wood release with ease using Enma. Something naruto while albeit on a higher scale has only been able to accomplish. I speak of hashirama's perfect wood releasenot Yamato's. Also not even Susanoo's arrows could destroy wood release but only pierce it.
The ANBU acknowledged both Orochimaru, Hashirama, Tobirama, and Hiruzen of being far from any level less then kage. They state it was so advanced meaning only kage level ninja would have a chance in a fight like this.
While struggling to use his Enma in his transformed state, he was able to slip explosive tags on Tobirama and Hashirama without either noticing along with orochimaru. This shows his ability to employ stealth tactics in broad daylight without Kage level ninja noticing. Quite a feat.
Hiruzen didn't use Death Reaper seal just because it was his only seal, but due to the fact that it was the most logical and tactical seal to use. A normal seal would allow orochimaru to summon the 1st and 2nd hokage's again thus prolonging the fight. By using the Death Reaper seal he made it so Konoha can never be attacked by the 1st hokage/2nd hokage/and orochimaru.
Orochimaru who was his student acknowledged him as the God of Shinobi. While he may only be called the God of Shinobi in konoha, it is a testament to his skills. Furthermore Kabuto acknowledges him as the strongest kage of the current 5. (4th Kazekage, 3rd Tschukage, 5th Mizukage, 4th Raikage.)
While using clones he was able to smell Hashirama and Tobirama out in a genjutsu. This is quite arguably is one of the greatest feats for hiruzen. Genjutsu disrupts the shinobi's senses already, clones are only equal to 10% of your skills, yet Hiruzens clones while having disrupted senses were able to smell out hashirama and tobirama and capture them. That is like being blind, only having 10% energy, and beating mike tyson in his prime.
Hiruzen was known to be able to use 1,000 skills(genjutsu in the viz translation) not by ebisu but also sakura acknowledges it.
It was even stated that in his fight with orochimaru and previous hokages he was on equal footing with them. Displaying powers that are beyond that of Hashirama alone, Tobirama alone, and Orochimaru alone. (search bar ftw)
Iruka stated that the third hokage was "The strongest of all" meaning all previous hokages that came before him were weaker then him yes that includes Minato since he was prior to his current term.
It was said that hiruzen fought on the front lines of the Second Shinobi world war. For him to do that fighting against terribly powerful ninja's like Hanzo in his prime(he was stated to be the strongest ninja of his time), the third kazekage(strongest kazekage), and the third tschukage who we have seen is no joke. This only exemplifies his prowess being able to fight battles against these types of shinobi's while surviving.
Hiruzen stated that his powers were far superior to Tobirama before Tobirama's death.
Any sort of "This is why hashirama is stronger" argument only makes hiruzen look stronger. You have to understand that since Hashirama was fighting with full use of his powers under a perfected edo tensei(see manga chapter 520 or my section on why it was perfected) it only makes hiruzen look more impressive.
"well iruka's word is worthless since its iruka he is fodder"
Not at all actually. Ultimately it is kishimoto speaking through his characters. Just like when Orochimaru stated hiruzen was the God of Shinobi, that actually wasn't necessary at all in the sentence. He could of just said old age caught up with you but no he said he was the God of shinobi. That title is only shared with the Sage of Six Paths meaning its a far superior title then someone thinking your powers were a fairy tale.
I'm not even gonna get the 1st and 2nd databooks involved since the manga provides so much proof of his status. He rightfully deserves the top ten status through feats and his history.
This isn't too say previous hokages don't deserve top ten or your top ten is weaker, but its to give credit where credit is due. Hiruzen even though he was last written about 13 years ago still proves to be a more capable ninja then the majority out there.