Comparing Destiny to WoW is, uh, misguided? This is such a slippery slope because at some point you might genuinely start to believe content in any game is equivalent to content in another - and make no mistake, it doesn't work like that.
WoW is the number one MMO in the world (for the last 13 years...) with a huge pedigree, and millions of people paying 15 dollars a month to play it on top of the 50 dollars they pay for expansions (the argument that you can buy game time with gold is silly because someone out there is paying the 15 dollars, even if its not you.) WoW could very well have gotten a sequel at this point if they felt that was the right approach, but clearly they felt constantly iterating on one client was the way to go.
Just because the two are multiplayer and feature similar design elements (stats, ability trees, raids, etc) does not mean development is remotely comparable between the two... Destiny is a physics-based fps designed around gunplay and traversal with completely different design philosophies and problems it needs to solve. In effect theyre nothing alike despite sharing similar terminology.