I see all the current classes as being fairly well balanced when it comes to their levels and relative powers.

Assassins gaining assassinate at level 35 is pretty balanced in comparison to what other classes get in and around that level, as well. Some classes have a slow developing power curve... starting out slow and then gaining more power faster as they get to the later half of the levels (i.e. Mages)... Others gain a lot of power early on, but then learn less things as they progress throughout the levels... and others still gain a steady amount of power as they progress.

Level sitting has its advantages, but also has major disadvantages. It all depends on WHY you are level sitting. Are you an empowerment character, not wanting to progress any further before hearing from your God? Are you a human assassin at level 35, stalking and assassinating everyone within your range? Distention helps to counteract this in some way, though I believe too little of a degree from my experience... however I assume it was designed like that because some people, quite honestly, don't level sit on purpose. Sometimes they have a string of bad luck, mob deaths, and whatnot.

Generally I believe level-sitting to be a bad idea, but that's only because of my playing style. I don't find it desirable to sit at any one level for any period of time. I always feel that striving for Hero is in my best interest.

Most of the time people are truly missing out on a lot if they level sit. Most every class does get some cool ability that should be on a person's high list to attain up at 51, or at the very least the mid-high 40s... With the possible exceptions of Healers, Rangers, Shaman, Thieves and Trannies.

I think level sitting is perceived to be more of a problem than it really is.