I'm actually more familiar with @Iheartnathanos's definition of the phrase "high concept," being something that has a striking and easily communicable idea. While you might say the notion of exploring a fantasy setting's afterlife and discovering that both it and its denizens are elaborate fabrications created by an automated realm created by a heretofore unknown pantheon of distant creator beings is "striking," it falls pretty short of what one would typically think of as "easily communicable."
As for the rest, yes, I'd say the relevance quotient of Shadowlands is overall pretty low - not as low as WoD's ultimately was, but much lower than its surrounding expansions. Even BfA, still my personal least favorite expansion of WoW, is more directly relevant to the ongoing story-arc than Shadowlands is.