I agree it's the right choice, so long as they can sustain the rate of release. After all, there's always going to be bugs and balance issues no matter how long they test for. My concern is that 7.3 is going to hit and they're going to delude themselves into thinking that the next expansion is less than six months away, and we're going to have another massive wait with no new content. But we'll see.
I don't think most players are going to be able to exhaust all the content that Legion has. It is orders of magnitude more than Pandaria had, and that kept people busy for a while. Doing all of the content on one character took a long time. Then I got a few alts to 110 and suddenly I was in way over my head.