There are a number of factors to consider when judging a company's first-party output.
There's the number of studios they have and the number of people they have working on games.
There's the time-frame (like how comparing outputs from 2005-2013 doesn't match up against a system which lasted from 20006-2012 before being replaced).
There's the relative quality, diversity, and uniqueness of the library.
And then there's the little issue of the split in development resources.