Now i get where you have your confusion.

Fireball sorc are further then orb max range.

Which mean that you cannot tele arround the fire sorc cause when you start to tele TOWARD the fire sorc. Well the fire sorc is already gone. While you tele on a field of hydra. True you can cast orb but fireball sorc is already at least a screen away so if you orb only thing you will hit is air and hydra will hit you.

You cant hit what you cannot reach. Fireball casting is very fast.

Just like you said any one got their patern and so it's possible to guess where to cast fireball to hit a ice sorc while it tele.

On the other hand, the ice sorc cannot tele arround the fire sorc since the ice sorc will never get close and no matter how much you understand the patern of the fire sorc it wont make you magicly get near. Which mean you cannot hit and that mean you cannot kill.