I'd disagree here, Bethesda are like 8 studios. They alone come close to Sonys entire 1st party output quantity wise
Number of studios doesn't matter by itself. If you had to pick between Sony Santa Monica and Tango GameWork + Roundhouse studios, you'd almost certainly want to take Sony Santa Monica.
Buying Zenimax brought Microsoft up to 23 studios. Some of those studios are primarily working on PC or mobile games. Some of them are just ridiculously tiny.