TBH out of all the 'named' leakers, his track record is still the best, so he's a little more trustworthy than other similar folks. Even though everything any leaker says should be taken with a grain of salt.
Grubb was the closest to the Spartacus leaks after Schrier.
Supposedly the Xbox thing is a Cloud focused thing (or at least it was months ago) and MS recently established a cloud gaming focused team. So, if that thing is real, it's probably nowhere close to a public announcement, unless MS want to reveal a CG trailer and sit on it for 2~3 years like many of their current in-development games.