Honestly, I don't see the big deal. At any given point, creative folks are going to have multiple fires in the iron and work on a variety of different projects with a variety of different partners, sometimes even in the same genre. Doesn't mean they're all interchangable. I mean, look at comic books. The same writers and artists go back and forth between Marvel and DC all the time. Jack Kirby, Marv Wolfman, John Byrne, Frank Miller, etc. Doesn't mean Superman is going to turn into Spider-Man and vise versa. In the end, it's just a matter of logistics. If you can manage two franchises at once, more power to you.