The problem is this game has lots of enemies with elemental resistances and even inmunities, but almost none with physical resistance or super high dodge, so in the long term physical-damaging classes have a easier time. Players can put elemental resistances above his magic armor, but there is no phys resistance, so phys works better against them too. Lots of weapons and skills have cc debufs and so. 1 lvl in geo gets you the slow cc, no armor save, no int required. So rangers, warriors and rogues are going to be much more effective in one to one. Period. No discussion here.
Even so, I like mages, I even made an all-mage party (The summoner uses elemental pets and the warrior uses staffs with warfare to blow that pesky magic armor, switching damage type if neccesary. A pity the shield but...) and it is very fun. There are enemies with low or no magic armor. Lots of CC to mess with the enemies and plenty of fights that require switch skills and damage type and think about who you attack to. I do not even remember have to examine the enemies in my previous playthrough. It was like shot, crush, bomb, all the time. It looks like another game.
You can even switch your damage type using the respec statue in Lady Vengeance to adapt to each dungeon if you like.
Most players know this, but since this is about advices for magic-users...
About stats, do not neglect your wits nor your memory, most skills have long cooldowns and some of the best require 2 slots and source ( even you can use skin graft or apotheosis do not count on it).
Concerning damage vs enemies with no resistance, i concour that fire-geo damage outclasses any other. Pyro is all about raw damage. Fire-geo has the advantage of explode and works well with savage sorcery (plus hothead) and torturer. Geo has very effective effects like entangle, petrify or slow (no armor save) and set surfaces with cc effects with poison and oil. Geo-fire combos does damage and agravated damage with poison and explosions. Also, Epidemic of fire and Pyroclastic are superb when used with apotheosis.
Water-air combos does little damage, but you have the shock-stun to cc enemies and it is easy to create surfaces with rain and bloodrain.
Even I admit that Hydro has his uses, you can use Aero against a burning enemy to shock and stun-lock, but water and blood drowses them. Only few air skills work against fire (like pressure spike). The good thing is that you can use skills like turn oil, poison wave or any fire skill to create clouds and apply fire damage to previous water or ice surfaces and add even more elemental damage (But not viceversa).So, most of the time I use geo-pyro and Aero in top of them, with Hydro only to heal if necessary.
Huntsman, warfare and scoundrel are useful to have, if only for erratic wisp, smoke cover and cleanse wounds. And The Pawn!. Not much use of necromancy, even it is very nice. I use vampiric hunger instead if necessary.
source:
http://divinityoriginalsin2.wiki.fextralife.com/file/Divinity-Original-Sin-2/fO6mOM3.jpg
