See Steparu’s videos of soloing a Lv200 party quest monster to see why.
From what I understand, you can be knocked out of Safety Wall. So bosses could be given a knockback (several already have one) and use it conditionally on Safety Wall users right next to them. The knockback could have significant wide up to prevent the skill from being entirely useless during these fights.
If that is not correct, they need some other way to bypass this.
