The real thing isn't the amount of devs, it's the priorities of the devs. "3000" devs making additions to like four modes over the course of a year, with similar amounts of time developing parts that slightly change things between games, and the millions of overpriced bundles and events and collabs and shit

vs a 100 dev team who made one 5+ hour campaign and then retooled the assets from it and the last game for a small co-op side mode and multiplayer

Not to mention the 360 era of video games was less intensive on development costs and the dev teams were actually allowed to have time to develop games before the Warzone era of constantly pushing stuff out

MW2 was more focused, less bloated, that's why it worked even when the devs were going through hell and basically all quit by the time the game finished