That's a relatively poor argument though
@Banat, considering that doesn't work for everyone. Even if they can't be hidden in units, they can be shielded from Melee units by simply waves of stuff between them. And when the only good answer is "KILL IT!" then there isn't much flexibility in that, or tactical use. It's just saying "Wizards force your hand to kill them at all cost" or else they can make a free new army?
Summoning certainly, as
@Malisteen said, far outclasses other options by far. Except in rare circumstances when all you need to do to kill an enemy hero/monster is the last 3 or less wounds, and you want to take that potential risk. And even then, if you're in range for the Missile you're probably in range to summon a unit that could just charge them. As long as you have room to place the unit. But if we're going to make board space the only premium that is limiting summoning then we're all doomed anyways.
Again echoing
@Malisteen, it doesn't greatly effect the normal game since it's the difference between starting with them deployed and just setting them down later. For comps, it's certainly going to be a hurdle to try and balance summoning and with the simplicity of AoS it's hard to say what you could apply to fix that.
Limiting spell dice isn't really an option any more.
Limiting number of summoned units is, although IMO that makes a big issue with zombies merging units, I guess that's a minor issue if you assume people are summoning better units than zombies. Even still placing the "one unit per wizard" rule only forces the wizard to go big or go home, and there would never be need to summon any unit that is not considered the "Best" for what is to come.
Where as summoning a unit of Skeletons might make an impact on the game, it's far less than a Terrorghiest. And they are not terribly much more difficult than each other given how many bonuses can be claimed with a handful of models on the board.
But things are just going to get muddled the more restrictions that are placed on them. I don't have the highest of hopes for competitive AoS, but that doesn't dismay me simply because I wish to play for fun, and scenario building more so. I wouldn't mind a competitive form of play, as long as it doesn't supplant the alternatives completely. Which is what that Jervis article was about: the imagined need to force "Competitiveness" in a game that will always have flawed balance, and which can be so much more when simply applied in a different style.
Want to limit summoning? Determine the limits per match. Playing a huge game with 4k points equivalent from before? Maybe you don't need to limit summoning. Playing only a handful of units and you happen to have a necromancer? Limit him to 1-2 units, or only zombies or something. Just don't expect people to want to play if you are going to say "The rules say it's ok!" to justify when you do things that aren't going to be enjoyable for both sides.
Oh Snap! 
