If it feels like you're exploiting a loophole, then don't assume it's allowed unless your GM explicitly allows it. And please don't argue in real life about such things. Ruins the table's mood.
No, I'm the GM. My player wants to pick up Wholeness of Body for that "healing meditation" vibe but is otherwise uninterested in ki spells. His plan was to retrain his current first level feat into one of the prerequisite feats, then retrain his fourth level feat into Wholeness of Body, and finally retrain his first level feat back into its original selection. I did not allow that, but I said that when he gets to sixth level he can pick one of the Ki Strike or Ki Rush, then retrain his fourth level feat, then retrain his sixth level feat into either Ki Blast or Abundant Step. Quite frankly, none of these higher level feats key off specifically from one of the lower level feats, so it doesn't make his character more powerful than the other PCs.
Also, discussing builds does not, in any of my tables' experience, ruin the mood. It's part of the experience.
You're explicitly not allowed to retrain into something that you wouldn't have been able to take initially, so no.
Are you talking about Retraining requiring prerequisites be slotted into lower level slots than their successors? A good point. This would make it impossible for the sixth level feat to cover the prerequisites of the fourth level one.