When did Rian Johnson say that? He’s obviously afraid - it’s in Hamill’s performance, it’s in Luke’s behavior, it’s definitely present in the moment where he talks a good game about burning down the tree and then doesn’t do it because he’s scared to.
Yes, he wants to stop the cycle, but he’s also scared to do it. And eventually he learns that his method of stopping the cycle is a bad one anyway, because while his intent was good, the way he went about it wasn’t.
He’s not “suddenly” on Ahch-To because of fear, it was always a part of why he went there. Fear, Shame, Anger, Sadness… all of that is mixed together in his motivations to cut himself off and stay cut off.
Him having Leia’s saber stashed away in there isn’t a “plot hole.”