The reason why I say this is cause through natural progression Naruto and Sasuke have become extremely powerful.
The only reason why Hashirama and Madara got so strong is cause they were at war there entire lives so as they fought one another they became stronger and stronger.
In a sense you could say If Naruto and Sasuke(Seeing as they are so strong through sheer progression and training) fought there entire lives in war and improved through that aspect. They would be A LOT stronger than Hashirama and Madara.
We have to remember the theme of the series is the newer generation surpasses the older generation and going off of what has been displayed. Through natural progression and talent the newer generations have truly outshines the people before them.
To Sum it up for those who don't understand:
Naruto and Sasuke at 16 are stronger than Hashirama and Madara when they were 16....