Ok. well that makes sense, but if it's in the sacred realm shouldn't link have had to help it in some way?

After all, ganondorf entered the sacred realm and it became a dark and corrupted place(or whatever it says exactly) Wouldn't rauru need some help with that?
if you believe the time line theory, then the dark realm you go to in ALttp should be the sacred realm right?
It had a lot of thing to fight.