Legion introduced groundbreaking features that have lasted up until this day, those being Mythic+ and World Quests. That's slightly different than continuing to carry those additions over.
Legion also had a new class, order halls which were beloved, artifacts which changed the way you played your class by adding new abilities and playstyles as well as adding on tons of cosmetics and quests tied to that, a complete overhaul of pretty much every spec, Suramar styled campaign and questing which you continue to see this day in the form of max level campaigns, a completely new honour system, legiondaries, fishing being made into actual worthwhile content, Dalaran Underbelly PvP content, the introduction of micro holidays, the introduction of mega dungeons.
Then in patch content we got Mage Tower, The Deaths of Chromie, amongst much more.
To say Legion scraped by is completely disingenuous. There is a reason the expansion is so beloved. It is literally the most groundbreaking and revolutionary expansion to this day.