I guess you are partly correct. Although I would argue that 'are now' seems a misleading statement since it has actually always been that way with desert-elves being the only one karma role. They always required a request into staff to pre-approve the role and check for availability.
I wouldn't say that they are more tightly locked however, if you have 1 karma then 'approval' for a role is simply a case of whether or not there is space for that particular role, be it due to clan limits or magicker limits. 2 and 3 karma roles require either special application or having met the criteria for those karma levels which is significantly more difficult to achieve than earning the longevity point for 1 karma and dropping a request into staff to ask about space.
It just so happens that we now have two races occupying tribal space and therefore tribal procedures. I will say that thryzn and their position in the world are, and always have been, very much in the hands of the players. Make of that what you will.
