That wasn't the manga stating it. That was Hachibi's personal opinion. He was saying that having more chakra doesn't make you stronger. There's a lot to consider, more than just chakra reserves.really even after the manga just said the number of tails does not determine its strength
I stop reading after the 1st few things you said about 3 tails and 6 tails.:shrug:yea but back in the normal naruto and early shippuden when naruto got angry he wud release some of the fox's power against sasuke at the end of the retrival ark he faced him with 3 tails of chakra and he was pretty epic (for back then anyway) and when he fought orochimaru he realeased 6 tails of the fox's chakra and almost killed him. may have no relevance just thought id mention it lol, and like someone said in this pst just because minato only sealed half away doesnt mean the fox's power wouldnt return over time
Kyuubi cant be permanently seals. No dealmon can be gone forever. They even state that if a Demon were to die it would just reapear. That means that they MUST exist and they cannot permently die or be sealed. So they must regenerate the chakra they lose. I doubt minato really knew about sealing demons that well, be he did do a great job holding Kyuubi down lol.minato said he ll permanently seal 9 tails power... so 9 tails power is sealed... but isnt less thn 8 tail