What are you talking about? Fireball is 2AP and you aren't just casting a Fireball. You're dumping 4-5 AP into the Incarnate, which then has 4AP to spend that turn. After the first turn you're at an AP advantage. You end up with a pet that also gets a single target ranged attack as well.
It's been mentioned elsewhere, the values have changed over EA, and you'll notice spell scaling reflect the original AP cost. The changes could be correlated with the existence of Elemental Affinity. Thus, fireball behaves like a 1AP action despite having the initial cost of 2AP. Furthermore, if you compare abilities across the board and bring in other factors (resistances, spacing, cool downs, memory, and whatever else) things only make more sense if you reduce spells by .5 or 1AP.
Advantage is solely determined by whatever the current game plan is. If the game plan is to kill things as soon as possible, then you may not have an advantage, you're possibly at a disadvantage or have achieved parity. If you can't kill things instantly and have to do a drawn out fight then you are at an advantage unless the tactical situation changes then you may be at a disadvantage.
In the current meta, most situations would say that you're at a disadvantage.
Mages that focus on casting elemental spells have the advantage of being able to cast more spells initially, and uh...congrats? That's all they can do, and it's overall less effective until Act 2 when the good stuff unlocks. Even then, they won't be dealing as much damage with the same spell for a while.
You can break through almost anyone's magic armor as an elementalist within the first turn in mid to late Act 1 and still have enough AP to CC them depending on your build. That's pretty much parity with everyone else. Your burst damage also exceeds or is the same as everyone else.
Also no idea what you're talking about in regards to the scaling. Fireball scales with INT, Pryo and level when you're casting it. For Summoning, it's just Summoning and level. It's not disingenous pointing out how when a Mage that focuses on X element first is at a disadvantage. Because they are. Unless you keep dumping into MEM, your slots are finite anyway, and your spells don't exactly have short cooldowns.
There are a few ways to look at it, but the important thing you should note is that fireball's base damage is that of a 1AP skill. Your multipliers are going to be far less effective on a spell that has low base damage.
Your comparisons really don't match up without considering the entire situation.
