In my opinion, adding any kit that has the ability to kill other players in 1 hit seems like a bad idea. Most FFA maps have significant height differences throughout the map, which makes this weapon become far too strong. I feel like it will ruin the experience of players more than it will improve them.
That doesn't mean I wouldn't like to see the mace on CC at all, I just don't think it fits in FFA. Perhaps if Duels ever gets added again we get a chance to test the mace there :p