Hate to say it, but I disagree to an extent.  I've noticed that established members tend to earn more merits than members with no reputation whatsoever--and you could argue that more senior members tend to make better posts, but I don't think that explains it all.  Newcomers have to work probably 1.5x as hard as Legendaries or Hero members to earn merits (at least I'd estimate it to be that much extra effort).

And the fact is that there's a finite amount of merit floating around at any given moment, and add to that the fact that there are people who don't give out merits for whatever reason, and the fact that there are so many active members, and you get the result that it's pretty damn hard for lower-ranked members to earn enough merits to rank up.  I don't know where that thread is that listed how many members had ranked up for a given week, but the last time I looked at it, there weren't many members at all moving from Sr. Member-->Hero and Hero-->Legendary, not to mention that going from Jr. Member to Member isn't easy either.

So it's very easy to say "just make good posts and you'll earn merits" but that's just not the case.  You have to do that, of course, but there are many other factors involved.