I apologise for repeating myself, and Radagast is not responsible for such changes, so he should not be the one to take the brunt of our disapproval.
Nevertheless, as Django pointed out, in the current state, both realms have taken a relatively big hit to their flexibility and their strength to adapt to certain situations. Because of this change, the reliance on runes and towers is bigger than it should be, in my opinion, and it makes the factions more monotonous.
The majority of fans were very pleased with the previous implementation of the Old King Dain and Young King Dain. Furthermore, I cannot really remember reading many or any balance complaints on the English forums here. It was generally accepted and there were no complaints about it being broken, so I really do not understand why such a change was apparently necessary. It wasn't broken and didn't need fixing.
Currently, on the competitive level, people play Ered Luin the most, and if they don't they should, because they have by far the better heroes and more versatility than the other two dwarven realms combined. Compared to Ered Luin, the others are kind of one-trick ponies and feel a little boring/bland, in which the previous Dains provided some versatility to combat that blandness. To continue, Ered Luin can stage many plays via flanks and charges mitigating their frailty to a certain extent via pure speed, but the other factions had their leaders provide some sustenance. Especially Erebor, my main concern is Erebor, because they are an offensive faction, but they have the speed of a defensive one. If you want to be on the offensive, speed is just as crucial as attack. Iron Hills can soak up all the damage and still do decent damage on their own and therefore outlast a fight, but Erebor really hasn't anything particularly outstanding apart from the previous implementation of Old King Dain. Their damage is nothing insane, and their primary source of late-game sustain has now been removed. Dwarves are known for their tankiness, and to all degrees should have some of it in each faction that concerns Dwarves. This is just my point of view though, and I can imagine that it could be interpreted differently.
Dwarves were only OP in the previous iterations because they could get infinite heroic batallions (so glad that's gone), but the rest was fine really. I hope the Lord of Mordor hears our pleas