I wouldn’t say that makes it bad. Palpatine has always had some pretty convoluted, seemingly counter-intuitive plans. The way I see it, he’s constantly setting it up so that the people he’s manipulating can choose any one of a dozen possible options and still end up giving Palps what he wants. In Return of the Jedi, he tells Luke to strike him down in anger, but just a few minutes later he tells Luke to kill Vader and take his father’s place. If the former happens, the Sith gets a new vessel, and if the latter happens, Darth Sidious gets a new, stronger apprentice. Palpatine wins either way - so at any given moment, he’s goading Luke towards whichever path is closer.

The same is presumably true for Kylo and Rey. Having one kill the other will push whoever survives towards the Dark Side, while also ensuring that the stronger of the two is the one who gets to become the host.