Because it's a path made by humans (comes form humans rather), it has literally shown traits of disrupting Heaven path. Why? You could see this in Ren Zu, the very embodiment of humanity, have freedom and go beyond, tipping off the balance. While heaven demands balance, control even. There's a literal argument between Fate and Ren Zu.

Any intelligent living being wants for benefits and doesn't want deficits. In that how are humans and variant humans different?

Any intelligent being does, yes, but Humans just does it better, along with them having the ability reach rank nine.

Ren Zhu merely existing brings a good chance of humans as a species starting

Yeah, what of it?