it's all in the balance not in numbers of pets following you, for example you can have one super summon (one example of the build i stated for example) let's say that at end game he hit's 1k or multi summon with 3 pet's that hit 333 each or a fully fleshed necromancer summon as someone asked before with 10 skeletons plus a golem doing 80 damage each skeleton and 200 for the golem for example, in the end they would all be the same overall, so having multiples summons or one summon does not matter as long the balance is done with them not the number of them!
this would also influence people and make everyone not taking summoner since What is important in the end is the illusion of freedom and the importance of the gameplay of what makes the player feels good, because this is what the player is in the end doing, playing(at least most of them).
If we look at any mmo or mostly rpg games today, ( i will focus only on the dps pve aspect since is simpler to explain with it) we normally have only a illusion of freedom(at least in a good balanced game), if you take any dps class as you role is mainly to dish out damage the develop would create a content and calculate/estimate a overall base damage/stats value for that specific content of the game he created similar as "do X amount in y seconds " simple as that even if you are using a big ass axe, or a sword and shield, or magic or daggers or bows in the end that is what you are needed to do is dish out "x amount of damage in y seconds" and this is the first step of overall balancing: the classes needs to "dish out x amount of damage in y seconds " to pass-advance in this specify content and it does not matter of how you do!. (of course i'm taking the standard scenery here, no one please come saying that you can "keep avoiding" the bosses atk and kills it in 10-20hours, because we know that is not like that, nor the content was not made to be played like that!.)
the develops tries to match the classes to this value that is needed by giving us the illusion of freedom and this illusion is given by drawing GOOD POINTS and BAD POINTS of each class and their respective skills!.
for example the main factors when considering dps pve aspect!:
(again i'm only using dps pve to show a point.overall the number of "Layers" is more complex with as many steps as the develops want it to be )
if the skill damage is dealt by range, it should have a increase or decrease of that base value to reach the base estimate damage needed for the content .
if the skill damage is magical, it should have a increase or decrease of that base value to reach the base estimate damage needed for the content .
if the skill damage have add on effect, it should increase or decrease the base value to reach the base estimate damage needed for the content .
if the class is agility class, it could have less damage but higher frequency of attack to reach the base estimate damage needed for the content .
Again i'm only using the dps pve aspect for this, there is more steps and is overall more complex than i showed above but i'm trying to simplify! for example: one of the "layers" i skipped is the "add on effect on skills we have different types of CC like slow, stun and each one would give a up or down in the "overall base estimate damage" needed for the content in the end making it all too big to explain,
So why i called "illusion of freedom"? since as i said in the same very example that those classes would have in the end good and bad points that would tilt the balance in favor or not in them doing more damage and the reason is because if the game is IF Balanced enough all those " end values of each class" in the end should be pretty similar to each other so a party of dps should be able to do their role even if you did not use a specific combination of classes, thus the illusion of freedom is formed it does not matter what dps you are picking since they should be able to do their role of dps somehow , of course this is talking about a balanced game something that is hard to come by, and thus creating the "famous METARACE", where one or more classes dps (for this example) is so higher than the other in the base estimate damage for the content that it makes it be better overall than all other choices, something that should not exist!.
i'm sure that is even impossible to explain to everyone each step and each "layer" of balancing since the limit is only done by how far the develops wants to go with details in their balancing since even needing to have a specific combination of classes to clear a content is one of the layer of balancing mmo as well(we see this a lot in trinity mmo), some people even call "optimal setup" to clear a content for example, it is also a layer and could be of course add in the mix of balancing but this involves supports and tankers in the mix so i'm gonna skip since i'm trying to keep it to dps only so overall in the end the DPS classes needs to reach a base line of value with all other dps classes with their own different abilities to have a game balanced and this is why "the balance of classes" most of the times never ends in the modern setting of mmo, it is too complex and have too many "LAYERS" but this is not a bad thing too.
So going back to summoners, in reality my previous msg seems far delirious in a sense if i could say because what i wrote was more or less bringing all this aspect of "balancing" to the summons as well and not only to the summoner!, so how could they add multiples "Layers" and the illusion of freedom in a summoner and thus making summoners builds balanced with each other?
Simple replace the layers i pointed out before for something as i stated in my previous post like :
one bigger summon
multiple smalls summons
summon+summoner using skill
Summon fusing with summoner and only summoner using skills
in the end all those "DPS summoners" options would have their own downside and upside in the overall "layers" of damage just like differently classes would act with each other and of course all of them should also be in conformism with all others classes and reach a "basic standard for the content not more not less than other classes " and of course you could add support summons, defensive summons, and everything else in the mix as long you have it "balanced" with each other following the same rules for balancing the summoners and his summons as when creating and balancing those support and defensive classes classes for the content.
(ps: again i'm only used the dps aspect in this, when you add support skills-defensive skills of course this would tilt the balance in the other way by making it hard for those classes to reach the "basic standard of damage to clear the content", even more in a trinity system game, and this is why people make parties for parties content, by taking a number dps class that have a higher than the "basic standard of damage to clear the content " but "lower base survivability for the content" and mix with it defensive and support classes that have a lower ""basic standard of damage to clear the content" but "higher base survivability for the content" you reach the balance wise situation or in pure dps aspect games, where everyone still needs to have the basic standard dps to clear a content, there is still a lot of other layers to mix things up like mobility, defensive abilities,cc's and so on. )