Bolt Weapons don't matter in 30K - 40K yes, 30K, not so much. It results in about 1 extra kill per turn, and at Bolt Weapon range, that's about 2-3 a game. It's the Shieldwall issues. Got to admit, I missed the bit about Eternal Warrior - maybe that will be fixed however, considering that the Traitors now have Chaos empowered rules to back them up.
Plus, the rules were never that balanced.
And if you're having trouble as Emperor's Children, you do have 9 automatically appearing contemptor dreadnoughts. Spare a thought for Sons of Horus (at least Night Lords get access to at-Initiative rending and Night Fighting). And in regards to broken, Iron Warriors - 4 Heavy Support choices is pretty fucking brutal. As is objective secured heavy weapon squads with Shred Heavy Flamers. Or all outflanking Alpha Legion, with access to things like Gal Vorbak.
And if you want really broken, play against Mechanicum.
There have always been stand out choices - Flare Shield/Ceramite Spartans, Terminator Troops, Contemptors, Typhons, etc. The individual rules of the armies didn't make up for it - the slight nuances between the different legions in Book 1 were not that strong - hell, look at the rage against Firedrakes and Vulkan. Now, nothing to be seen.
The same choices in any list is going to be equally strong. It's just what you want more out of. The only trick is that the thematically CC armies are gimped, and that they have to jump through hoops to get the benefits of their legion rules. But the legion list is the same.
People who say otherwise don't play at high enough points levels. The game has never been balanced to play at low points levels, hence the points tax on Rites of War, and points tax on Minimum unit size. What kills marines still kills marines - namely, Terminators, Contemptors, Typhons and a few things on the side. The one thing gimping some armies is compulsory moves - EC challenges, for example. That can be fixed easily. Don't take expensive units, and don't get in combat (because this is 7th edition, shooting is king).
The difference between higher tier armies is much lower. High level games essentially boil down to who can rock paper scissors the enemy rock paper scissors first, then turn on the points tax units. Exactly like 40K. It's not more balanced, but its less imbalanced. The lowest end of the spectrum is still more than capable of fighting against other legions. Struggling with your Bolter hordes against Iron Hands? No shit. That's because you're firing Bolters against Marines, when you've got 3 S7 AP2 Blasts on an AV13 wall, or S5 AP5 Pinning, or Fire Raptors, or Contemptors, etc etc.