I can answer this for you. Attack and defense definitely do matter in the Taken King, as that is how we are rated for combat instead of light level. The new light system takes the average of your attack and defense, and certain activities will check this light number to ensure readiness. So you will likely not be able to wear a set of blues, or greens to do the new end level PvE (I could be wrong though, because VoG was originally done by most in almost all blues).