Knowledge is power!!!
I believe that people dont understand why hiruzen is the strongest hokage and im thinking about making a thread. Basically this is why hiruzen is the strongest hokage. He was trained by both the 1st and second hokage who were leaders of the senju and that clan was said to be a clan with a 1000 skill (or some shit like that). If you notice hashirama had loads of scroll, scrolls that if you are elected hokage you are entitled to and i believe one of those scrolls is what naruto stole at the beginning of the series.
Now Hiruzen being a part of the sarutobi clan who were said to have natural talent in learning ninjutsu fast, its reasonable to say due to his old age, plus this natural ability he has mastered all the scrolls/ninjutsu's that existed in konoha. He has done something that not even his 2 former masters did in their life time. Further more if you look at the db he is the only person, yes only person to get a 5/5 for all 3 forms of ninja art and this speaks volumes. No wonder he was called the professor.
Now because he was the student of the 2 hokages he knows their techniques very well, so much so that if he was to fight them he would be able to counter and we saw this. The weakness of the Kokuangyo no Jutsu is that apart from the eye sight being taken away from you, all your othe senses are there and because hiruzen being the student of the 1st knew of this technique and its weakness he used his nose (sense of smell) to track hashirama;
Secondly Enma is a good counter for mokuton and we have seen this. Hashirama used the same technique as edo madara when he first used the mokuton. The technique was Mokuton Hijutsu: Jukai Kotan. Enma not only made mokuton look like a twig it also protect hiruzen;
Tobirama being a master of suiton jutsu. Hiruzen knew this and was able to counter his Suiton suiryudan, with doton doryuuheki;
The reason why Hiruzen is the strongest hokage is NOT solely based on raw power but knowledge on his counterparts to defeat them in a fight. Its his knowledge on his teachers abilities that will allow him to defeat them in a fight thats why he is strongest amongst them. Note the word
amongst them because i believe people dont understand this.
If we were to give hashirama and hiruzen 10 top shinobi's to fight in a 1 vs 1 situation, i believe hashirama would win majority of his fights and i cannot say the same for hiruzen. So whilst hiruzen is the strongest hokage due to his knowledge on his former teachers, if we were to take this a step further and place them both outside the criteria of hokage hashirama is stronger, but if were to revert this and place them in the criteria of hokage hiruzen is stronger.
Hashirama is stronger but for reasons stated above hiruzen would most likely beat him majority of the times. Its not raw power that makes hiruzen stronger than hashirama
EDIT: Getting tired of posting this over and over again when it seems people cannot think for themselves