What aegis does is effective let you survive at lower max hps. They have eased this a lil bit by giving us vorseals. I would say that if you wanted to attempt to do endgame without aegis you would have to stack more hp to counteract the increased dmg that you are going to be taking, as well as once you hit 50mdt either through gear or shell that you also stack mdb. /run helps a lot when you know what specific type of element that is going to be cast against you, just use the appropriate runes and valiance.