During the duration of rescue beam these abilities flying gets supressed which consistently causes issues for my team when i am trying to help them. In the case of ivy the flight might literall be a setup for a game deciding Stun, on vindicta it might be for getting a stake and on talon hitting...
An easy fix would be to have the wall check for an instance of the slow to see if it should apply the package of damage and slow if that is not already the case (was when i last tried but maybe the slow issues still exist mentioned by SaintYin). Without some changes there is very little reason...
I have noticed this with pocket Ghost aswell, it could be argued both are not projectiles by some margin due to their size but then abilities in general should not be blocked by it unless they are said to be "Projectiles" in the description.