Firewall sorc are useless in pvp as everyone would be moving arround and by time firewall would deal dmg any none noob would be gone.
A zon/necro they could shoot/cast during time sorc wait to cast firewall again.
Any melee would just rune to the sorc and attack since no melee in duel are slow the firewall wouldnt be even close to be something usefull.

Firewall is useless in pvm cause it is hard to control, Inneficient against crowd unlike meteor. Meteor can also do much more dmg. I still have to put 8~ points in fire mastery and my meteor lvl 26 is already 10k-11k dmg.