I personally think that part of the reason that we still have 'power' armies is because we're not limited to taking 1 HQ and 2 troop to get any other good units. Now we can just take elites with HQs, or heavy supports, or even a detachment full of HQs. This leads to crazy things like Commander spam or Terminator spam. I, personally, prefer the old system of the FoC from 5th. I know it still had its gimmicks, but everyone had to pay that troop and HQ tax to get their awesome elites and fast attacks, and the max number of HQs was 2, so no Librarian spam or Commander spam.
I know that system wouldn't work today what with the a lot of armies not being able meet minimum requirements on their own(Skitarii for example have no HQ units, Imp. Knights are purely LoW to my knowledge), but I still prefer it regardless, as I never played any of these smaller supplemental armies
On top of that, adding in extra gimmicks like Chapter Tactics and Strategems just keep adding to how much power a player can push out in a single turn to almost guarantee their own victory. We never used to have these, and we relied wholly on the units we chose to bring, but now each one matters less individually because we have things like the Doctrina Imperatives of the Skitarii, giving your entire army between 1 and 3 BS or WS with less of a sacrifice than the gain, and their units were already really effective without such bonuses(granted that was their 7th edition benefits, however they'll probably get them back with their own codex).
I guess what I'm really trying to say is that I'm feeling a bit hipster-ish/old school, and that all these little army wide gimmicks like Chapter Tactics and Doctrina Imperatives and whatever anyone else has, is just packing more and more power into the game, creating immense power creep, meaning that the first turn advantage is bigger than ever, and that I don't like any of it.
That, and I'm still super sour about the T'au in their current state; it really sucks when the best models you own(Riptide, Crisis suits) get ruined, meaning you have to either fork out more money to have a fair game anytime soon, or you just can't play at all.
But I suppose, GW is a business before a games developer, so their priorities are money before balance.