actually it is fact that people are in a stagnant progression. I don't think that anyone who played EQ1 at the start can deny that it was insanely hard in comparison to FFXI. People tend to forget this and think FFXI is the only truly hard mmo. Which amazes me. Yet, Sony changed the game as time changed. The game is, iirc, 3 years older than FFXI, and has see na lot more major changes. I can't give hard numbers (that once chart that put subscriptions of mmos proved to be greatly false 'cause they based if off of forum activities), but with 14 servers, and 1 type of server overflowing to the point they had to add another, says to me they were a lot smarter about how to keep players playing.
They also in the beginning had a very stagnant progression (eq2 even at the start), but both have built their progression a lot better without it being Wow-fast. Progressing to some degree gives people something new to do. But when only 10% get to keep doing those new things while the 90% are still stuck doing content 6 years old, then it's pretty safe to say you're going to start loosing subscribers at a much higher rate.