That’s strange because it never bothered me while Leia being Luke’s sister does for the same reason.
I think it’s because Boba being a modified clone doesn’t really shrink the universe as much as provide context. There were millions of clones fighting in the war just 20 years ago, of course some would pop up as bounty hunters if the Empire sent out a flyer. It’s a retcon but it makes sense if you recall in the OT Boba Fett isn’t a special bounty hunter, he was just in the right place at the right time.
Whereas Luke/Leia is just terrible all around.