Artifact questlines, Class Hall Campaigns, Suramar, the Illidan questline, Balance of Power, Pillars of Creation, Class mounts, WQs, Mage Tower, M+, Raids, Broken Shore, and Argus.
Suramar was IoT, Broken Shore was TI, Argus was Krasarang, M+ is a better (and repeatable) version of CMs, MoP had an extra raid to start, WQs are just dailies but they were relevant the entire expansion because of Paragon caches and legendary farming, Balance of Power/Artifact progression was basically the Legendary cloak questline, Mage Tower was an improved version of Proving Grounds with rewards that were unique to 36 classes instead of 3 roles, and MoP had the farm and that’s about equal to the mission table.
They had pretty much the same amount of content. A lot of Legion was class/spec unique and repeatable though.