I wouldn't proclaim Etihad's First (including A380 First Apartment) as "World's Best" either. It's a big claim to say it's "World's Best" and it falls short on a few metrics (most notably ergonomics) - and I say that as an Etihad Platinum who has flown Etihad in the premium classes extensively.
I prefer flying Etihad's 777s to the A380 due to the better ergonomics of the old First class seat - with the Etihad A380 First Apartment you get an somewhat limited seat and a not very comfortable bed (some of the bed seats are now starting to slope slightly with age now too, which I really stops me sleeping).
Service and catering can be really mixed on Etihad - a few crews are great, most are pretty ordinary, and some are really sub-par for a premium cabin - catering can run to the underwhelming or terrible (with insufficient catering at times) although they do deserve points for anytime dining. Consistency is missing.
Ground services have been lacking, although the re-opening of a First Lounge may improve that.
Perhaps the most disappointing thing about Etihad is that if anything goes wrong, they are pretty terrible at service recovery/remedy, even for their top tier Etihad Guest members.
While I have not flown The Residence (and unlikely to do so given it's only a incremental improvement over First for an over the top increase in price), I feel pretty comfortable based on my direct experience in saying that Etihad is an interesting airline that is making improvements and clearly seeking the "World's Best" mantle, but is not yet there.