I wouldn’t mind if Minecraft Dungeons and any new spin-off game would be Xbox exclusives. They’re not main Minecraft. That’s different games and Mojang is a first-party studio. In 2014 they committed to keep Minecraft as a multiplatform. Dungeons is a completely different take.
Also, I would release Minecraft Dungeons later than May 2020. Maybe September or even at launch of Xbox Series X|S already with cross-play/cross-save/cross-progression (Xbox PC), Jungle Awakens and Creeping Winter as a base content and all of these other minor updates which came after May 2020 and then they could start with that Season Pass which launched in December. At least review, receptions and scores would be better, because most of the people complained about not so much content at day one.