I’m not sure Anakin disproves that, though. He very well might have been able to resist Palpatine alone, but he chose the Dark Side. I think the importance choice in one’s fate is something that shouldn’t be understated. Rey could easily fall the same way as Anakin and Ben, and she’s been manipulated by Palpatine the same way, but its her choice not to that decides her destiny.
The trouble would then be that Luke’s decision to isolate himself on Ahch-To is really stupid. All he has to do that whole time is tell Kylo that his fate isn’t set in stone, and that he gets to make his own. Instead, Luke tells Leia AND Rey that he essentially is irredeemable because of what he saw in his future.
“This is not going to go the way you think.”
“I’ve come to confront him. But I can’t save him.”
He never tells Kylo to reconsider things when he projects himself on Crait, so there’s clearly something there that can’t be undone in terms of his destiny. At least until Luke becomes aware of the dyad.
EDIT: For clarification, all of this in TLJ is likely residual of setting things up for the DotF script. Kylo WAS indeed supposed to be irredeemable in Episode IX, with no chance to be saved. So TROS desperately needs a reason, even if it is kinda half-assed, as to why something as unavoidable as fate can be overcome by BOTH Rey and Ben.
TL;DR - Destiny may set the stage, but it is the characters’ connections that ultimately define their paths.