Dude he was Orochimaru's student and witnessed him casting the jutsu, of course he knows how to use Edo Tensei.
Not assumption, Outer Path puts Rinnegan users outside the cycle of life and death hence why they can control souls as shown with Human path and Naraka Path.
Hagoromo was able to summon the Kages without a sacrifice, and Sasuke can simply dig up some graves if he wants to put the souls in physical bodies.
He witnessed him casting...right, but this is not just another jutsu. Its Edo Tensei. Learning it is not as simple as witnessing someone doing it and pulling it off yourself on a whim.
Now you're using a vague statement in your case, when both users of Rinne Tensei in Canon died, or in Obito's case, where left on borrowed time then died. This statement alone is not enough to prove that a Rinnegan user, even a natural one, can pull off the use of Outer Path with no drawbacks.
Calling upon souls, okay, but shoving them into a dead body to bring it to life. But shoving it into a body? True, that's what the Edo Tensei does, but again, there is no proof Sasuke can use that, nor that the Rinnegan allows him to "shove a soul into a body.
You're just presenting well built fiction as fact. It makes sense, okay, but making sense doesn't make it Canon.
