It's pretty rare when I actually fundamentally disagree with
@LewTheShoe. I understand his perspective broadly, but I think the real point of separation is how we view the purpose of the Xfinity and Trucks series. I view them primarily as, for lack of a better term, minor league. A clear and delineated step down from the very top level. I see value in them serving multiple purposes as both developmental and 'senior' circuits for drivers who attempted Cup but don't have a place in it anymore. I don't see much value in them being continually dominated by current Cup stars in their prime. Limited appearances are cool, but I consider the era in which Kyle Busch, Carl Edwards, Kevin Harvick etc. were running for Xfinity and Cup championships simultaneously as the worst era for the junior series.
I don't see Kyle Busch dominating the Xfinity series and Kyle Larson running WoO races as the same at all on a competition level. Largely because the latter is so specialized that Larson is at a disadvantage to the regulars of that series when he drops in for a visit.
Having said that, it isn't on Kyle Busch to limit himself, and he's done nothing wrong. It is the sanctioning body's job to define the series, as they are now doing.