Microsoft had 3 generations of showing a strong 1st party lineup, they never delivered. There is absolutely no reason to believe it's gonna be different this time around.
We've been hearing about MS beefing up their 1st party for 15 years now.
Nope. No reason at all. They went out and acquired studios left and right pretty much for shits and giggles, because in reality they have no intentions of turning GamePass into the biggest service in gaming, or even if they did, they know that a steady stream of quality content independent of 3rd party reliance isn't particularly vital to that endeavor at all.