Part of the reasoning for leaving old Legendary equipment (and some Exotics) behind is to create variety (we shouldn't all be using the same thing). However by removing the opportunity to bring the old forward, they have reduced the list of weapons and armour that are practical to use. We will therefore see many people using the same "OP/Latest go to guns" from the new list. If we had the choice of old or new (and the new ones are viable compared to old) then we will get variety as some stick with old favorites and some move to the new. By banning the old they only raise concerns that the new weapons will be like HoW (do more base damage but are worse in almost every other way).