There are various upsides to this imbalance. Max level players are able to complete lower level content with ease, allowing them to swiftly complete missed quests and achievements in earlier zones, and can travel through zones without being constantly attacked, since mobs will only attack players several levels higher than them if walked directly into. Max level also makes it possible to solo earlier group content such as dungeons and even raids, making farming loot such as mounts far easier, and for those interested in a challenge opening up a new subtype of play at slightly higher levels.
5% was admittedly an exaggeration, just felt that low. I'd say it was probably closer to the 30-40% range. It was Artifacts of the Blacksilt, spent a good 10-15 minutes killing Blacksilt Seers to get two damn idols to drop. A quest that had me killing Elder Brown Bears for bear flanks also took quite a while, though that was less due to drop rate and more due to how spread out they were.
Anyway, however you choose to get to the addon's menu, choose guide list and then pick the zone you want to quest in. There are some zones that will autoselect based on quests in your log, but not all guides or all quests are set up that way. (If you don't want to switch to a guide that auto-pops up choose "not now" or "never") As you can see in the screenshot, there are various categories of guides. Most max level content (such as Argus) is found in Achievements rather than leveling.
Something to keep in mind as well is that this will make enchanting materials more valuable, since it is likely most players will now simply scrap their boe greens instead of getting them disenchanted. Also redundant dungeon/raid gear can be scrapped rather than traded to the (guild) enchanter in the run. Less stuff gets disenchanted, meaning there will be less ecnhanting materials, meaning their value will rise. All the more reason to DE rather than scrap as an ecnhanter.