So, making the Skywalker blade also distorted serves two purposes:
- continuity fixing. It acknowledges the ending of TLJ, where the lightsaber was split in half. Rey repaired it, but in an imperfect way, leaving the blade unstable as a result. The actual kyber crystal IS seen when Rey holds the pieces of the broken saber. So it’s less of a retcon and more of an actual consequence.
- storytelling tool. Rey wielding a crackly lightsaber represents her inner conflict and her struggle with the dark side. It mirrors Kylo’s blade, and also serves as a subtle irony when Ben finally claims his grandfather’s weapon, but it’s damaged and imperfect.
Thanks Knight of Kalee that explains it well.