The essence of Futarime no Rikudo
I think Kishimoto-sensei sets characters' power level as a measurement if their determination. Naruto is determined to help others see through their deception and acknowledge who they really are (as how he defeats Obito). Hashirama is powerful and defeated Madara at VOTE because of his determination to protect Konoha, even if it means sacrificing his friend. Hashirama and Tobirama lose by far to Madara in the present day because their determination to protect Konoha has somewhat shifted to Naruto and Sasuke (such as when Hashirama goes as far to ask an Uchiha to stop Madara and give him charka and a jutsu).
Now, regardless of how powerful Naruto, Sasuke, Hashirama, and Tobirama are, they all fall far below Madara's power level. This is a testament of how powerful Madara's determination is to establish a new world of winners, peace, and love, a world Hashirama failed to create. Madara has held unto this dream for about a century or more. This far exceeds Hashirama, Tobirama, Naruto, and Sasuke's lifespans. For cherishing something as precious as a better world from childhood until death is what empowers Madara to becomes as powerful as he is today. His power level is on a completely different league from everyone else because Madara is, in essence, a personification of "not giving up". Some people may be against the world Madara envisions because it is a Tsukiyomi. However, compared to the shinobi world right now (Under the current shinobi system, Team 7 were made to face the Demon of the Mist Zabuza at 12 years old!), Madara's version of winners, peace, and love topples over all systems (as representative of his strength surpassing everything).
