Yes, i'm perfectly happy to accept that he has gotten a powerup. But how? How did madara suddenly get so much stronger? Yes, he absorbed sage mode from Hashirama, but why couldnt he have just done that as an edo?
Also, What the hell does RInbou Hengoku even do?
Answers in the form of smug madara fanboys will not be accepted, and probably neg repped.
Madara got a few power-ups, but he's also more powerful than we know. He's never shown his true power, at least not for many years. Look at some facts:
Early Life
1. Madara had an unusually high ability with the sharingan
2. Madara was the first to unlock MS and first to obtain EMS (rare and very powerful)
Battle at the Valley of the End
1. Madara was
trying to lose. He was not fighting to win, and he still put up enough fight to exhaust and weaken Hashirama
2. Madara gained Hashirama's power, inserting Hashirama cells into his wound
After the Final Battle, as an Old Man
1. Madara integrated Hashirama's cells into himself more completely, even gaining a form of immortality
2. Madara gained Rinnegan (and, as we saw with Sasuke, every eye power-up resulted in increased power overall)
3. Madara unsealed the Gedo Mazo, summoned it to him, and used it as a source of life energy
After Revival
1. Madara had Hashirama even more deeply embedded into his body
2. Madara was revived as a young man, not a weak old man
3. Madara gained Senjutsu chakra from Hashirama
4. Madara has regained the first of his missing Rinnegan eyes
These are just the power-ups that
we know about. It's very likely that there were other power-ups as well, since Madara has spent so much of his life researching legendary sources of power, bloodlines, etc.