Mages are best DPS on all of the following.
Gron (195 EDL)
Cragskor(205 EDL)
revenant(210 EDL)
Event legit and event 5*(210 Seasonal)
All banebrands and the 6* version(220 stones)
Gelebron fire and ice crystals(220 healers)
If that's not useful endgame DPS class then idk what is

Full fire mages aren't going to get current event, 205, or 210. Full ice mages aren't getting 195, banebrands or many of the past event bosses. A mixed build is best dps on none of those bosses.
Post a screenshot of your gelebron crystal kills as your sig, otherwise that shouldn't be on your list. Oh wait you don't have a screenshot of that cause nobody cares who is best crystal dps
I've never had a necro kill myself but it is very impressive. On mages being worst endgame dps, I highly disagree, if you build your Mage right they are formidable on any boss
I didn't say that mages are the worst endgame dps, but they're overall definitely below average. Assuming high tier endgame gear among all 5 classes: worst on mord, 4th or 5th on necro (depending on whether swarm is resisted), 3rd or 4th on proteus, same with gelebron, 4th or 5th on 215, either 1st or 4th on 205 and 210 depending on whether ice or fire
Level 220 mage- InnerCircle of Rhiannon
Necro, proteus, unox kills
http://www.celticheroes.net/profile.php?hero=runvs