Blizzard sseems to be cutting stuff more often than not.
TBC was probably the best finsihed expansion, with 4 patches, and big raid, SWP with huge story impact too at the end.
WotLK did finish, but it felt like the Ruby Sanctum was a bit short.
Cataclysm - they didn't really finish the revamp, it ended up only being partial
MoP - not sure
WoD - they cut Farahlon completely
Legion - they cut Thal'dranash (but spun it as replacing it with Argus, I think it was a cut)
BFA - HEavily reduced 8.3 content.
Do they need more time? or more staff? TBC ended surprisingly well, but if you normally play beta, you tend to find out a fraction of what gets cut.