Kurama was talking about Uchiha's chakra.
He said the same when Sasuke was inside Naruto's conscious mind.
Nothing do about Madara and Obito 's chakra.
Uchiha's chakra are not same as others' chakra.
Refer to
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what did Kurama said of Sasuke current real power.
Not all Uchiha, but some that reached that level.
That was why all the tailed-beast (bijuu) did not trust any human and
the bijuu hated to be controlled by human, especially Uchiha's powerful eyes,
most probably was that SO6P can control the Juubi, but
did not use bijuu's power, that's why Bijuu respected SO6P,
and later when Naruto saved all the bijuu, in return, Kurama finally respect
Naruto's way................................................