Walls seem slightly off, this is due to some prior changes that were made early on however this is not representative to the original game nor does it seem to be well documented.
Currently walls above wood wall, irrelevant of tier seem to go down at the same speed, my original impression was that this was a bug or something that was underlooked by development but as mentioned earlier it seems some major change took place that shifted things very strangely.
Mage's ice walls should be very hardy against everything minus high level dispels and fire spells, this goes the same for earth and stone wall minus the corresponding elements eg: earth vs earth.
Update walls to reflect identical values of MSM based on spell buffs/changes that have taken place, this includes removing void weakness to all walls. Void was never intended to replace dispels, storms or elemental weaknesses, teamwork is necessary to defeat all obstacles and the current schema will not work for guild matches.
For further deliberation, no one from AOL > GS > MSM ever complained about walls, so I'm very interested in hearing more about where this change was inspired from.