8th edition is the most I have seen GW try to balance the system in the past 20 years. You are always going to encounter power gamers. And honestly, if you think 5th edition isn't without its issues, then you may need to take a closer look at the game...
5th wasn't perfect, every edition has had it problems but over all 5th requires the least amount of effort, it was a lot more balanced than 4th ever was lol.
I might also be using power gamer in a different way to you. Take a cleric in Neverwinter, basically a one man wrecking ball in neverwinter nights, power games option of choice because it removed just about all risk. To be more specific 1st edition of D&D as a system, was the least power gamy, as you really needed a party, vs say the 1 man armies of 3rd D&D.
Have a look at the mechanics of the game, 5th estimated distance vs premeasuring, foot based infantry that can move faster than vehicles, Mortal wounds that can be done on mass, pinpoint accuracy in deep striking. These are all power gaming features as they remove the risk of anything going wrong. In 8th, your biggest problem is the dice, and you get sooooo many of them now and so many re-rolls that even that's some what negated.
As for Balance, well just because everyone can drop a bucket of dice, doesn't mean it is balanced, the person going first in that case has a huge advantage. I've never been tabled 1st turn in 5th. I can have a bad first turn and still come back. I see far more games going down to the wire in 5th than in 8th, this speaks volumes to systems balancing than just evening up the number of shots the army can put out (bolter rule change for example).
I would also question if GW is really making an effort to actually balance the game, if we look at say patterns that keep poping up, new models+ruledates = podium finish in tourneys, then nerf, new models+rule update for another faction = podium finish, follow by a nerf.... That sound more like a marketing strategy.
Sure they pay lip service to some of the least used units give them a buff, stopping short of making them compete against NEW units then pop them in a box set.. again, sounds more like marketing than balancing.
Even this thread is kind of proving the point, if they were actually focused on balancing the game, then I don't see how one of the
most iconic things in the whole franchise can end up in this state.
but I think we are getting off topic, something needs to happen with Termies, something like only AP-3 or more affect's their armour save, that would make them tanky again.