Six Paths chakra has been a thing even before Juubi.
Obito when he was about to kill Konan alluded to himself (Madara, actually) having power of six paths when he combined Hashirama's chakra with his.
For one Obito isn’t a credible source on what Six Paths power is since he’s parroting Madara who learned everything he knows from the half true Uchiha Stone Tablets
Also, It’s a common thing in manga for the word “power” to be used in the context of abilities and/or raw power.
Izanagi is an ability of the Mangekyo Sharingan, an ability passed down from Indura, that was a derivative of Hagaromos own Dojutsu.
If we go by that logic “Powers” from the Six Paths have existed since the introduction of the Sharingan and Byakugan.
Hagoromo, when talking to Naruto, stated Madara awakened the rinnegan which is a derivation of his (Hagoromo's) own chakra's power.
His Chakra’s “Power/ability” is not the same as the literal power of his chakra.
Again “power” is often supplemented with abilities in manga.
The Rinnegan is a product of mimicking Hagaromos power via the mixing of Asura and Induras power
Six Paths Chakra is specifically Juubi Power, which is why Hagaromo can give it out because he was the Juubi Jinchuuriki, just like how Obito could let Kakashi use it after his experience as the Juubi Jin.
That chakra Hagoromo referred to was Six Paths chakra.
He’s not referring to literal chakra, like I said above he’s referring to an ability granted by his chakra, the rinnegan.
Something Madara gained by mimicking Hagaromos chakra with his and Hashirama’s chakra.
There's no way Madara would have activated rinnegan without Six Paths chakra.
there’s nothing in the story that states or implies this.
Madara proclaimed "So this is the Power of the Six Paths" when he became Juubi Jinchuriki because he activated another level of six paths power. One that grants him the Six Paths Senjutsu.
“So this is the Power of the Six Paths” is not something someone would say if they were just getting a boosted version of something they already had.
It’s something someone’s would say if they’re experiencing something for the first time.
We also know that Madara pointed out that Naruto has Six Paths Senjutsu and Sasuke gained a Rinnegan but boasted how he has both (which at the very least means in Madara’s mind having a Rinnegan doesn’t automatically give you Six Paths Chakra which he would know from personal experience since he awakened his Rinnegan.)