I actually think the opposite, up until the climax. Having a caretaker-type person who isn’t important in his own right allows you to have the echo of Palpatine still be an active antagonistic force long after his death, while allowing Kylo to be the central “bad guy” for the majority of the film. It only breaks down at the climax, where if you can’t have a confrontation between Kylo and Rey since he’s been redeemed, you really need a genuine physical battle against a galaxy-threatening foe to tie into the Resistance story.