well, it's call following the sequence. 2, 4, 6, 8, 10, __,
what's the next number that will follow 10? based on the sequence of the numbers we know it's going to be 12.
It's the same with what happened in the fight oro vs the third. He summon first hokage then second hokage after that what follows? The answer is third hokage.
it cannot go one way or the other because nothing in the manga will tell us so
We are not baby readers. Kishi doesn't need to explain everything, kishi expects us to know this much and to follow his story without him having to explain a lot. There are things in manga that do not have solid answers but we can make solid answer as readers from sequence that happened in the manga. They can still be called solid proofs