Here's the thing though, if you make so players who have played for longer have a distinct and continual advantage over those who don't, you will never see new players. I started around HW's release. Why would I continue playing if no matter what I do, someone from launch is ahead of me not because of their individual skill, but because they picked up the game before I did?
And we need new players why again?

What is better, if game sells 1 million and keeps running for 10 years never getting new players but also almost never loosing old ones. Or if game sells 1 million each year for 10 years, but only 200k players stay subbed longer than month?