Here we go again.
1. 3rd classes are not nearly finished yet. Every week Gravity still does fixes on them.
2. These classes were not designed to be played without the so-called Renewal game mechanics. No private server out there has full Renewal game mechanics emulated yet. This results in them trying to modify the 3rd class skills to their own custom formulas, which results in no private server having the same 3rd classes, basically.
3. They are buggy and make the server unstable. There is no official 3rd class/renewal emulating by eAthena yet, just some community-made one called 3CeAM which most of those "awesome" servers copy-paste on their server. This project is still unstable, unreliable, unofficial and just not good.
So don't expect them any time soon.