The BS started with Natuto saving Guy. Might Guy unlocked the power of Gods(last gate) with the ultimate consequence waiting for him in the end.
A consequence that was completely stabilized law of the verse for a decade plus.
But Naruto completely negates all of that just by tapping his chest...
Okay.
It wasn't just Gai surviving the 8th gate either. For me it was the fact that most of the ninja world laws of nature/charka that Kishimoto spent so much time and detail into creating throughout the series kind of went right out the window once the Rikudo power surfaced.
Your example with Gai is one:
Madara using Susanoo with no eyes. (say what you will but every explanation by fans given is not proof but speculation)
Naruto being the child of prophecy then later Sasuke being Indra transmigant for plot's sake.
The disappointing Juubi (who seemed more like a wild pokemon then an omnipotent being spawn from the original source of chakra)
Madara being Black Zetsu'd then turned into the biggest mistake Kishi could ever create.
That giant black sword that was said to have created the world gets shattered by the power of friendship with no repercussions to the world itself.
Obito himself: is he dead? no he's alive...now he's dead, nope he's alive again thanks to Narujesus. Then he dies, then his spirit comes back to give Kakashi his rikudo and Uchiha power (will never live that down)
So many thing went wrong in the end but I guess it's to be expected when you are literally running one of the most popular mangas for 1.5 decades.
OP: You are entitled to love absolutely anything and everything about this manga, but that doesn't mean everyone shares your opinion in this matter. It was a little better than your average Shonen manga and I will leave it at that.
In addition, all the power scaling went through the roof far too quickly and haphazardly to meet deadlines.