How arcane subtlety/elemental precision works?

Does arcane subtlety works on fire/frost spell? the guide here on nost say it wont. viewtopic.php?f=44&t=1440
For lv up are those talents a ''must have'' for mages? I get so much resist vs mobs 2-4 lv up, i could easily kill they if i dint get resist half of the time
Im thinking maybe the best spec to lv up(doing quests) would be get those 2 talents(5 points) and put the rest on frost, this way i got a chance of killing high lv npcs
For lv up are those talents a ''must have'' for mages? I get so much resist vs mobs 2-4 lv up, i could easily kill they if i dint get resist half of the time

Im thinking maybe the best spec to lv up(doing quests) would be get those 2 talents(5 points) and put the rest on frost, this way i got a chance of killing high lv npcs
