Snow Angel, Bug Hunter, Class Tester
Yes, hello. I am here to throw a wrench into everything you thought was true!
Really it depends on your definition of "best" for farming class, but if you're looking at the most efficient then the best farming classes are actually ones with the highest sustainable burst DPS. Which is basically your soloing classes. I've explained this before but it was a while ago, so allow me to do so again. The main reason for this is respawn times.
Say you have Class A, a single-target high DPS class, and Class B, an AoE class designed for farming. For simple math, let's say Class A and Class B can both kill 3 monsters in 30 seconds; Class A does it one at a time and Class B does it roughly all at once. On the surface, they'd be seen as equal, but because respawn timers are determined for each monster, Class A will come out ahead in a sustained farming session, Again, for simple math, let's say a monster respawns 10 seconds after its HP hits 0. Even if both classes kill 3 monsters in 30 seconds, Class A will have started the respawn timer for the first monster far earlier than Class B did. That means that at the end of the 30 seconds, both classes have killed 3 monsters, but for Class A the first and second monster have already respawned while for Class B, all three will respawn around the same time (40 total seconds). By that time, Class A will have had the first two monsters respawn and can have killed one of them. So at 40 seconds, Class A has 4 total kills while Class B has 3.
Respawn timers means that in terms of pure efficiency, a single target class will actually be a better farmer. However, it's not designed with farming in mind so it may not be as accomodating or as easy to use. That's why people like myself, who know that a single target class may be a more efficient farmer, will still choose a dedicated farming class for farming needs. It may not be quite as fast, but if it's easy to use (or use mindlessly) for farming then it's more appealing.
Believe me, this was definitely an issue we had to work with and around when we built Vampire Lord.
Regarding Glacial Warlord, that was one of the three Rollback Classes. That was such a long time ago, though, that I don't know if the issues would still be around. I suppose I can talk to Arklen and see if a version of the classes can be released that has the original skills/functionality, but I wouldn't count on it.