Couldn't it just be that MS is going to release the console a couple of months after the PS5?
I seriously doubt they delay release unless something out of their control goes very wrong.
On the subject of the dev kit situation I just remembered Phil's comments in the Eurogamer X019 interview: https://www.eurogamer.net/articles/2019-11-15-the-big-xo19-interview-xbox-boss-phil-spencer
Phil Spencer said:We also did just ship the development kit, which is another console.
Phil Spencer said:I know what you're saying, but I will say from the team's perspective, shipping the dev kit is as much work as shipping a retail product. You're shipping thousands of them out to partners. It is a dedicated piece of plastic they're gonna plug in and develop for.
So this suggests the (first real hardware?) kits started going out a couple of weeks ago so will take time for third-parties to take delivery and take stock (read leaks!).