Did you ever noticed the AI to destroy a Wall?

[Keneth]

I use Lina and Reaper in turns and the other two almost never get any action. On the odd chance that both Lina and Reaper have 1 round of rest left at the same time, I usually just use underground blades. Blocking the enemy can be easily done using phantom/summoning abilities/iceball/totems/demon portal/etc. and they all fare far better than any wall.