Exactly. According to physics, achieving light-speed with mass beyond a photon is equally as impossible as reaching absolute 0. I don't get such rants. Most battle manga and comics do this.
The chakra was inside Zetsu not Obito. Also Zetsu is Madara's own essence. The fact that Juubito could control Zetsu over Madara and after performing Rinne no Tensei and having the Juubi extracted is unbelievable. Also even if Obito had access to the Kyubi chakra, that doesn't compare to Madara's near complete Sennin form. And lastly, Madara countered a Haraishin blitz. How reasonable is it that Obito could do better?