Really ? You either have to look at Nintendo's output or just inform yourself better about third-parties. From the top of my head, the only third party that could be compared, in term of variety, would be Ubisoft.
I mean, just from this year, one that could arguably be one of the worst years of Nintendo, they managed to release two party games, one social application, three 2d platformers, one 3D arcade shooter, one tower-defense, one action-adventure game, five JRPGs, one rhythm game, one FPS, one vs-fighting game, one remake, one tactical-RPG and a freaking drawing-learning tool for kids.
And I'm only counting retail games here.
Who exactly has a more diverse output than Nintendo ?
Well, my post above apply to you too then.