That's true but only if there's only one team working on software at Apple. There's no reason to assume that the iTunes team needs to be the Photos team; while there might be certain dependencies on something like iCloud or OS X, the areas everyone complains about tend to be clearly contained within a single app and there are well-practiced ways to deal with things like API changes.
That just means involving more people _right now_ won't speed things up. But you can "make 9 babies in 9 months" if you plan early and involve enough people. I.e. know how much Q/A people you need and hire them upfront.
