You have ranged and melee atronach's so why don't you have something for every situation? Range is never ever bad, and if you need a tank, use a frost atronach and you be the ranged. You are allowed to fight yourself as a conjurer you know, it's a pretty boring way to play just summoning stuff and watching them do all the work. Like I've said before, you have spells for every situation in every school, there is no point in bethesda making 5 re-skins of the same spell, more variety is no reason to justify it, they need a purpose.
I haven't gotten high enough in Conjuration to get the Storm Atronach so I'm not sure how they fight (melee, ranged, combination of both), but you are correct in that "you have spells for every situation in every school".
Like for example, Destruction:
You get a flame thrower at the start and not another one ever so it is pretty useless high level.
You get a single target ranged spell at apprentice, but don't get another one until expert. So until you can get that expert spell you are stuck with a spell that doesn't scale as well against your enemies.
You get a targeted AOE at adept, but it is only good in some situations. Not so much if you have followers etc ...
My point is at novice you have a melee summon (familiar). At apprentice you have ranged summon (flame atronach). You don't get another melee summon until adept so if you need a melee summon you are stuck with a wolf fighting enemies that one shot it. So you have the spells for every situation, but they don't scale so it would have been nice to have multiple types of summons at novice, apprentice, adept, expert, master that have different styles of attack.