Dungeon difficulty is focused on the assumption of all players never doing it before and are all geared somewhat closely on-level with with the mob levels they will encounter. Just because people can grossly overgear a dungeon and memorize the perfect paths/pulls to do it in less than 15 minutes doesn't mean the dungeon is easy. 4-man dungeons aren't catered to the hardcore minority, they are designed for everyone (including casuals). Hard Mode dungeons will solve your problem if you're looking for more "hardcore" focused content.