Microsoft wants to release 1 AAA first-party game per quarter and more smaller projects like Hi-Fi Rush/Minecraft Legends plus.
Considering that average AAA game take 4-5 years nowadays (and that's if all stars aligns) and you need 4 AAA game per year, 30 studios is minimum considering the fact that many studios are operating live service games and are not releasing new titles at usual cadence.
If they can manage a slate like this (consider ABK buyout completed)
2023 - Redfall, Starfield, Call of Duty, Diablo IV, Hellblade II, Forza Motorsport
2024 - Call of Duty, Avowed, Project Midnight (Compulsion), Contraband, Fable
2025 - Everwild, Perfect Dark, Call of Duty, Oddysey (Blizzard Survival game), Project Cobalt (inXile steampunk RPG), ZOS new game
2026 - Indiana Jones, Call of Duty, Gears 6, new id Software game, State of Decay 3, new game from Arkane Lyon (Deathloop devs)
etc, they can be happy chappies without more acquisitions. And I did not mentioned new project from Double Fine, Project Mara, new game from Mojang, Forza Horizon 6, more XGS games, The Outer Worlds 2, Age of Mythology, new Tango Gameworks games and potential games from Activision studios.
But I still think that there are strategic purchases they should make. Like Certain Affinity for example. Or studios like Crytek/IO Interactive/Avalanche/Asobo.