naaah. you should more look at it like „new systems“ without „systems“. at best you can call it a general overhaul to some long existing stuff.
for another new xpac they always need a feature list for that xpac, to sell it. you can’t sell products without an appropriate feature list. you can’t base your sales just on „new content (quest, raids, dungeons)“.
in the last few xpacs they introduced new „systems“, related to player power. in reality this means some story + some cheap UIs (conduits, essences, etc) + some items that support that system. since ppl not want this (player power related systems) they do their new „systems“, they use as a feature list for sale (which is needed), now as other (non player power related) „systems“, like new talent trees or new professions system.
in short, an xpac needs 2 things: content + some new and attracting features. this time the features are not player power related systems but overhauled core systems instead (talents, professions).
that’s all.