Agreed, but we’ve seen him want to kill her (via Snoke/Kylo) in movies prior. I think it’s acceptable to imply he wanted one of Kylo and Rey to kill the other to prove their worthiness. I think it’s worth it for how much it adds to their collective myth with such compatibility with existing canon. If Kylo is also apparently worthy then it also explains why the Dyad is so powerful to him- it’s the power of both bloodlines, an unexpected best possible outcome.

As an aside, maybe we want to use other dialogue to imply that all of his Snoke/clone experiments were only ever intended to be temporary hosts at best.