Phil Spencer and Matt Booty both said the exact same things. Game Pass itself is already the service, the games don't have to be. Having too many GAAS games on there defeats the purpose of having a subscription game service since it would be cheaper for the person to just buy that game if they want to have something to invest hundreds of hours into it.
Game Pass will be great for having focused games with a beginning, middle and end since the devs don't have to think about how to monetize their games, GP is already doing that. Having new content every month is more important than having games with super long tails and long term monetization implementations. That's not to say they won't ever have games like SoT, clearly they will, but those kinds of games don't need to be the focus.
Can you list the games against these categories, cause I'm still not seeing it.
Single Player - Ori, ReCore, Quantum Break etc
Multiplayer - Many of them
Co-Op - SoT, Gears of War
First Person Shooter - Halo etc
Third Person Shooter - Gears
Open World (with multiple different sub genres) - Forza Horizon, SoT, Wasteland 3
Circuit Racer - Forza
Open World Racer - Forza Horizon
RPG - The Outer Worlds
cRPG - Wasteland
2D Platformer - Ori
3D Platformer - Psychonauts 2, ReCore, Crackdown
RTS - Age of Empires
Simulation (Flight) - Flight Simulator
Survival - Grounded
Action Adventure - Lots
Narrative Storytelling - Hellblade, Tell Me Why
Minecraft lol
He forgot fighting games with KI. I didn't list everything obviously, just examples.