All damage-only PBAoE shouldn't have a cast time. (Should work like Kats W, not Amumu's E)
It's incredibly frustrating to stop moving for .25 seconds to cast the incredibly short ranged amumu's E. Half the time you use it against champion's they've walked out of range in that time, and it put you about 100 units behind them.
Most similar skills (Point blank AoE's with short range nothing but damage), such as Hec's q, Kats W, Zeds E etc can be cast while moving, and it makes them feel so much better.
I think akali's e is the only other similar skill that does that.
