Unfortunately it seems everyone is going down a road of picking every army list and stating how powerful they are.
Every single army has the room to be overpowering, even the beasts of chaos mega tzeentch list with 'x' chariots can still be devastating,
and anyone ever played ogres with a tyrant and three hunters? its not pretty 'qwuhdoosh, qwuhdoosh, qwuhdoosh' "whats that? your knights are dead mate" then 6 dogs come running after you.
And i noticed someone talking about high elves being dodgy with their asf? well too right, regardless of what super weapon they have an elf is a squishy t3 girl, and they always will be, if they didnt asf then they would lose power to a tremendously low point.
Daemons have their ward save, undead are 'unbreakable', lizardmen are cold blooded, high elves strike first, skaven get their rank leadership... the list goes on. Every army has something which makes it an individual army, and if every single army was the bog same then this would be the most boring game ever.
Particularly on the tournament scene at the moment, for example i am attending one in warrington this september the comp rules are:
-no more than six levels of magic (i.e slann and level 2 engine is allowed)
- only one double of each special
-no double rares
and daemons suffer a -1 to their ward save for magical attacks, not to mention the 10 hardest lists play eachother in the first round.
Particularly on the tournament scene you cant make an army list which plays itself out (which is the definiton of a imbalanced list), for example daemons are bringing more and more slaanesh into the picture, i myself am using an oldblood on cold one with BoR
You've got to think outside the box with any army, every single army is balanced in terms of playability, its the army lists that can be so simply powerful that it takes a mindless drone to march it, but in general tournaments comp wont allow that anyway.
At the end of the day...You just do pit of shades
