level 1 fire wall will not help against pure str attking builds. Only one it would be effective would be chn pure str due to imbue. We would like to see a fire wall's mag abs help you with a warrior or a rogue. If all you want is to prevent kd kb, than level 1 will still work. Wiz nuke or warlock attk will still bring the wall down in 1-2 hits. Not much of a diff between level 1 or maxed. Only advantage you gain in maxing fire wall is for pure str chn characters. Don't say maxed fire wall will help against rogue kb kd.
The moment you cast a wall, they can just run out of range and kill you. Wall restricts you to a pretty small range. Level 1 ice wall can help with pure str attking builds. It will absorb all of the dmg of a rogue or warrior. Warlocks would have more trouble taking it down. It is useless against a wizard, but very useful against pure str chn, and pure int chn.