Well, using level 90 talents would be a start? 12% scorch damage is just way too much(cast fireball). And 5% combustion damage is way low. So I suggest make him read something like the Fire mage guide on this forum.
well on your best try ( the 8th minute one) no lvl 90 talent at all, he got 24 pyro procs and only used 15? 70 scourchs 16 fireballs ??
He should only use scorch when he have to move, even though you might have to move a bit on stone guards it's no excuse for this excessive use of Scorch.
He seems to ignore alot of pyroblast proccs, doesn't even bother to use a lvl 90 talent.
Quite frankly he doesn't know what the hell he is doing.
Tell him to go look up a class guide on icyveins or a similar site and then put him on a target dummy.
Fire mage's are so awesome on stoneguards he should be pulling way more then 30k, I don't know his gear level but even in 465-470 ilvl gear I'd say he should do around 50k on this fight. You are gonna have one heck of a problem when you reach gara'jal whit this comp beacuse of the tightish enrage timer if you have bad gear.