Obito was shortly away from casting the IT, if it wasn't for Naruto then everyone would be under IT, including Sasuke making him useless as he didn't have the Rinnegan at the time. Sasuke didn't have the TB chakra nor the ability to convince them to cooperate, you do remember that they only beat Obito because Naruto could extract the TB.
Also even then, the Sage wouldn't have given Sasuke all of his power, nor would Sasuke have been able to defeat Madara as he would have been killed right off the bat.
And that Rinnegan is that given power that you always criticize Naruto for having, he wouldn't have it without the Sage giving it to him like the Sage gave Naruto power.
So the same argument works that the sage could have given Naruto all the power as he was the reincarnation of the chosen heir, the only reason he gave Sasuke power at all was to prevent history from repeating itself.