What if Coruscant is just part of a sequence in Kylo’s detective style investigation. Instead of him finding the wayfinder in the temple, he comes across the X Sith sign on the ground of the council chambers, perhaps with an illustration of Vader’s castle, a clue to where to find the wayfinder.
From the slow Coruscant scene you would then cut to the luke and Leia flashback, Rey training, and THEN the Mustafar massacre.
That way you show a passage of time and fix the brake neck pacing.