I agree that some new abilities should be implemented. However I believe that given that there are a lot of supporting abilities already and some hero killer ones, the focus should be over all on mass slayer moves, and maybe building supporting as you point out.
The problem is not necessarily the lack of abilities, but the inefficiency of them. For example axe throw and thorn of vengeance dont do nearly as much damage as they should (like spear throw does); earth shaker now only works as a stunt, except on last level where the damage and radius is not much(and is expensive), same for the radius on leap.
Given the above, I'd like to propose adding a mass slayer move that allows you to have a passive area of effect damage, similar to how they implemented it to Elrond's level 5 passive ''Ancient Equipment''.
On a side note, I think you should be more specific with the abilities you are proposing to this threat to be taken into consideration by the team.