Why is WoW held up to some standard that every MMO has to "beat" in order to be successful?
Yes, WoW was extremely profitable, but does that mean the product was "good"? When WoW slithered out of Blizzard's diseased loins, the MMO industry was set back decades. If you really care about the "legacy" of TES or lore, or whatever, you should pray to god that this TES:O is nothing like WOW or even aspires to be.
Bottom line, WoW's recipe for success isn't the only viable business model, and "popular" doesn't always mean "good".
WOW earns lots of money, this makes other want to replicate it.
Now the safest way to do this is to make something like WOW but better.
The problem here is that WOW is huge and has lots of features, if you can't do better at launch date you don't compete, and you have to match WOW today not 10 years ago.
The other way to do it is to make something different, EVE online did this and it work well.
Yes you could do an compromise, something somewhat better and so much different that you draw and keep part of the customers.