You've got a point. On the other hand, a session musician isn't totally free in his creativity. He/she oftens follows a direction the band or musician hired him for. (exceptions there of course). Nowadays a lot can be done online / log distance. But if you look at Pino Palladino for instance, he also toured with a lot of big acts, I am wondering how that feels / is, you're not a real part of the band but still travel and stay with the crew. On the other hand, like with the John mayer trio, he is a part of the band for sure :)