I think it's as much about what happens off the ball as on it. Xhaka covers for Zinchenko in the buildup on the ball, and is tasked with making the late run into the box in the attacking third. Odegaard has much more positional freedom so he can roam looking for combinations and exploit space. Off the ball, Odegaard is often the pressing trigger in a 442 supporting the striker, while Xhaka is often much deeper alongside Partey. Looking at those season heat maps backs up this interpretation - Xhaka is relatively stationary compared to Odegaard popping up everywhere. You can even see how Xhaka tucks in at 6 quite frequently.
Having twin 8s with different auxiliary responsibilities makes us much more solid in defense and fluid in transition. When that balance is off, we look open and things get a little sloppy. Where it sometimes becomes a hindrance is when we are so totally dominant on the ball that the "6" part of Xhaka's role becomes redundant, and his limitations as a 10 become clear.
