Let's put it like this: if a user advances quickly through different ranks by acquiring loads of merits, they are obviously doing something right. Whatever they are doing, there seems to be enough people willing to reward them with merits to signal that they are doing a good job. I think that in that scenario, ranking up means you are maintaining and/or improving your post quality.

But if you were simply here a few years ago when theymos introduced the merit system and became legendary based on your activity alone, you aren't necessarily a quality contributor. You could very well just be a massive spammer that had the new system work in your favor.