Keeping necro and vex viable do not stop you or him from hunting new exotics. The reasons for them to do this are simple: 1) They no longer have talented game designers to come up with fun and powerful weapons that can compete with launch weapons. 2) They plan to resell old exotics in later expansions this year. 3) They are too lazy and lack the talent to balance all of the old exotics with new ones and they cannot be bothered to balance new content with all the old exotics.