I know what a Xanato's Gambit is, but I think where you and I are getting a bit lost is that for it to be a true one, all plausible outcomes have to benefit the mastermind. I don't see the events of attacking Earth as a "benefit" to his secondary goal of attempting for the Infinite Gauntlet, but instead becomes a detriment to his secondary goal.
For it to be a true Xanato's Gambit, then he would organize the events in such a way that, even if he lost on Earth, he would have no resistance in then claiming the Gauntlet, so that his first plan actually was laid out to only improve the chances of the second plan should the first fail.
Since his first plan was a DETRIMENT to his secondary plan, it was not a benefit. That is not even getting into the fact that this is mostly fanon until proven otherwise.
P.S. I will relent that it could end up happening, and we may learn more that makes it a much cleaning win/win, I just don't see it right now based on what we saw in The Avengers.