Imo the problem is far deeper than just summoning mobs. There is a balance issue in SoD and it's partly down to the disparity between casters and melees, but it is perhaps even more down to the 2 box thing, and the uneven interractions between different types of duos.
The classes are reasonably well balanced when it cames to soloing. In other words, a good tank is kind of, sort of, round about, vaguely equal to a good caster. Tanks may be super powerful, but when soloing a tough mob in an average zone, they take a long time to do so because they are not as fast as a caster, and they would take serious beating during it too and have to spend time to recover their health afterwards. So it kind of evens out compared to a caster who is quite efficient at killing things 1 on 1, but very squishy and depending on downtime with mana too.
The big problem is when you add a healer bot. Add a healer to a caster and it does very little to help. Add a healer to a tank, and you are now basically godlike. Look at zones like Highkeep for example. A good healer/tank combo can pull the entire floor, tank and spank it all down and the healer just ez-heals the tank and maybe does some AE if possible to help take it all down faster.
A caster combined with anything, can just not do that. Not only are they incapable of fighting large numbers of mobs, and summoning mobs, but mobs that are immune to root, fear, or db/flurry/etc are also generally out of bounds too. Especially if you are a pet class, because a pet can just not cope against those kinds of damage spikes.
The bottom line to me is that it generally seems like the best and easiest journey in this game is to just be a tank and druid/shaman.
It's a shame because I personally find the caster classes to be by far the most fun to play, solo. But when my high tier necro/cleric combo gets pwned by mobs that a t1 tank/healer combo can easily kill with their eyes closed, it makes me very sadface. And with a large part of the game (like the faction quests) involving mass farming of massive numbers of mobs, it just becomes far too tedious to do that with a caster when a tank/healer can just spank it all in large batches. (And when I say tank, even Monks can do it too). These uber duos get all their quests done quicker and easier, they get to kill FAR more mobs in the game, including even low tier raid content, and they also get far better XP when it comes to general duo'ing.
It frustrated me sufficiently that I have since abandoned my tier 9 necro/cleric combo and made a pally/druid combo that wipes the floor with anything. I still find it far more fun and challenging and deep to play the older combo, but seeing as this game is entirely about aa's/tomes/quest completion/and making lots of cash, then I am far better off just playing my new ez-mode combo and farming a bunch of 1m plat charms and 40+ tomes. So I found a solution, but it would be very nice if we could find a solution that doesn't just involve rerolling.