Well, I would make Shooters one thing, not just FPS.
As for the answer, depends on what you mean. 2D Platformers and Shooters have the largest volume of entries yes. But saturation is a negative thing, the idea of useless and detrimental excess. With the 2D Platformers, a TON of entries are so low profile people don't know they exist so I wouldn't call that saturation, which would usually indicate the idea of the genre in question sort of choking out others through sheer excessive exposure. And Shooters cirrently have a healthy variety in settings, styles, mechanics, so I would callit plentiful, not overly saturated.
In my mind, Sandbox games are the most saturated genre. There's plenty of great open world games that are good, but there's an excessive number of Ubisoft style nebulous open worlds that contribute little or nothing to anything, they just suck up budget and marketing real estate.







