That's exactly the point. WE don't know how much Senjutsu chakra it took, but the amount of chakra he took from each Bijuu, which even if you try to guess, will never make an appropriate answer. However using common sense, that isn't a 'little' bit, you can never argue that he just took a 'little'.
Naruto's Senjutsu power mainly comes from Hagoromo. How the hell would he power up such a thing with his Senjutsu power alone? He buffs himself through Kyuubi Chakra and combining it with Senjutsu.
Why do you think it's the latter and not the former? :lol
Sasuke using the Kyuubi Chakra doesn't make your point invalid, it just proves that Sasuke can use the just the Kyuubi Chakra because it's being enhanced through Senjutsu.
Your assumption as it being 'a lot' is no different form anyone saying he took a little.. Sasuke implied he could've gotten more chakra from the bijuus make your assumption baseless because we have no ideal how much he took or needed.
Sasuke and Naruto both have Hagorom's chakra, which is equal to Senjutsu chakra, Kurama doesn't.. All bijuu combine does, making Kurama chakra alone irrelevant.
Naruto doesn't power it up alone.. Sasuke also helps.. Sasuke couldn't make nothing more than a rib cage Susanoo after sending several people (7-9) through his portal, that's one of the reason he was burned by Momshiki. Then he absorbed all but three seconds of Senjutsu chakra from Naruto. Enough to heal his burn
and complete his Susanoo beyond the standard PS. That implies it takes anything other than a large amount of Senjutsu chakra.
No it doesn't make my point invalid only because Naruto and his Senjutsu chakra.. The feat couldn't be done with Kurama's chakra alone or without Naruto being in RSM.