I think we need Every troop (specially new ones) to get almost equally choices for everyone i.e. There should not be very powerful troop (like what now _Necromancer _is) that evry one can choose in defence or offence.
So is with _Vikings _that they are not very good at offence than Stunning Ogre.
Knocking back ability is Good, but it could be a second thought of anyone about Viking while seeing it for First Time.
What could be first thought is ability to Shield (ally troops and King) ,like Monks do, but in some other way(like hitting shield to ground, etc.)
And One thing more that - when Vikings knockback, then at that moment, any attack (near or ranged) coming should go back towards thier respective attackers (for e.g. cannon balls towards cannons & lightining stroke towards nacromancer or skeletons & bombs either from skull or bomb tower should return back even they are on the grounds & arrows from tower or archer or arblaster etc.)
This could make Vikings a Very Good choice for players in offence and/or defence among other troops.