"But if the current generation will always surpass the one before, then how would he stand up to his own second coming - Uzumaki Naruto."
this was never set in stone, not all new is better than the old.
I always expected the old would be better than the new as they were in times of constant war where powerful techniques were in high demand for SURIVIAL.
Just like in real wars the technology developed during then is far more impressive than in peace times. Most of the technology we use today comes from the advancements made for world war 2 and 1.
Moral of the story is; if need something really bad your forced to get it. Especially if your surival is in stake.
The infarmous phrase said by kahashi to Kakuzu was in regards to the wind rasengan. And the wind rasengan is the only jutsu we have seen in this time era of the narutoverse that is truely powerful and new.
Naruto will surpass the old powerhouses that try to copy the sage of 6 paths like madara, tobi and even hasihrama. Naruto making a new technique that is very powerful is proof of that. He also has sage mode something that will prove to be ace in the hole as the enemy hasnt understood how it works and what it does or how powerful it really is.
That being said just because naruto has the making of surpassing the so6p heir that doesnt mean everyone else in naruto's era can surpass their respective elders. The so6p was once in a lifetime and so is naruto by the look of things.
I think alot guys assume madara fought hasihrama in a lot of 1v 1 situtions but in times of war this rarily the case. The shinobi world though hasihrama was the best, the fire counrty though this and made hokage.
I doubt given how powerful hasihrama's techs are i doubt you would be able to face him solo hence madara used the fox in the only 1v1 situtaion we know of that they fought in. Not saying there werent others but whats excatly said in the manga is that senju and the uchiha fought. I doubt they fought 1v1s alot.
"But even Hashirama would've lost against Minato"
doubtful minato's weakness is attack options if you tank the rasengan he has problems. Hasihrama given his healing and chakra reserves would take minato no problem. remember hasihrama was talking on the fox so he can handle a rasengan.
Not saying minato would die either as he could just simply run away with his timespace jutsu but thats not really a fight anymore is it.