Recently i was debating someone, the topic was Adult Naruto's Kurama avatar vs pre kaguya fusion juubi, the guy was telling me that the Juubi from the past was more powerful than the one the Juubi Madara absorbed

From what I remember correctly when the Juubi was split in nine, the bijuu were born as babies and when time passed they became bigger and stronger, i know that they pure chakra so my assumption was that the more chakra ment that the Juubi was more powerful

I know that the one Madara absorbed had 1 to 8 at full strength (although gyūki left a small portion of a tentacle so bee didn't die) and just a half of Kurama (but come one it's Kurama, one half can defeat 7 of the 9 bijuu), but the guy told me that the past juubi is stronger because it had both halfs of Kurama

So can anyone explain me how does the Juubi exactly work?