Aside from the perks it does not take long to max out an exotic weapon, the newer version exotic start off at 302 ATT which is basically where you left off with the old exotics. Plus you dont have to trash your old ones anyways, if you get a new version from a Nightfall and so on hold on to your old one until youve upgraded your newer version enough. Plus upgrading exotics is a hell of a lot easier now.