It's not an absolute guarantee, but it's still a metric. I'm not exactly sure what's the point you're trying to make here?
It's like saying "Education doesn't guarantee good job and good life", you can even cite some examples like Bill Gate or Einstein as school drop out ... but again, what exactly the point to make there? That education isn't important and should just be ignored?
Sure, it's not a guarantee, but a game with a good sale still has a much better indicator and align with a "good" game than a one with poor sale. Just like you can be an A students and still end up broke, but in general those who received good education will have a better chance at having a good life.
Or we can stop pretending the world revolving around us and our own taste, and anything that goes contrary to it is of inferior qualities.
I have been enjoying FF14 for the last 8 years, and I hope that will continue. But I don't hold SE under any obligation to please "me", rather the moment they start producing something I don't like, I just call it quit and move on to other things. What important to a MMO is to make thing that the most people can enjoy, I'm not narcissist enough to think I will always be part of that group.
The day I depart FF14 I will wish all those remain and would come in the future to continue enjoying their time, not with bitter resentment that the game should burn in hell because it's no longer cater to my taste.