A necessary choice given the state of the game and reactions to what was shown. Between building an engine, leads leaving and COVID, there's just been a compounding effect on Infinite's development. Many games, especially huge AAA games, really come together in the last months of development leading up to launch. The pandemic's thrown a massive wrench into all of that.
I think it's a blow to launch, no doubt. Infinite was a huge pillar behind the Series X, the big game Microsoft would center launch around. It's not the *only* selling point, but a big one. The decision to delay was no doubt a very, very difficult one to make. Having known people who had to get projects done in time for launch no matter the costs, it took some balls to call this by the studio, undoubtedly facing down a line of angry execs. Maybe however it is just a sign of the industry maturing, and not just deciding to break the team in order to launch at any cost...ultimately, it's for the best for the game and team.
At the same time, expect news about other Xbox stuff that's been going around recently to come a bit later too.