Why do you think that shift would be so severe? Interrupts would still be there, as would the incredibly hard CC this game has. There might be a slight population change with all the casters who gave up coming back, but it would even out im sure. Basically, this would just even the playing field cooperation-wise. Instead of a pug having no problem with solo healers, it would be an even playing field. Casters would still have to work to avoid dying/cc/interrupts, but they wouldnt be a punching bag for people who sign up with friends.