In terms of relevance, Kizaru is fine. His presence in this story is one for the books.
One of the only antagonists who has history with Luffy in 3 separate arcs. Was responsible for the biggest turning point of this series, when the Strawhats had to split up on Sabaody. And now responsible for Vegapunk's death. His impact on this story is felt.
The only shame is we may never get to see what an all out Kizaru looks like, and that is a big big shame if you ask me. I'd trade that for character writing any day if I'm being honest. But objectively looking at it, Kizaru's character wasn't badly written at all.