And MF's E is dealt over the course of two seconds, rather than dealt (or at least applied in the case of Brand) in a fraction of a second.
But I see now that I should have continued on down that list.
More champions with similar or greater damage in a single ability than MF gets from her E:
Gragas Q (after some delay; full delay put's MF's E to shame, and oh, would you look at that, the full delay is 2 seconds, the same as the duration of MF's E)
Malz Q is only 10 damage short, deals that damage in a single instance, and applies a substantial silence
Maokai's E (impact and detonation combined) deals an extra about 25% damage
Have you seen Mord's W?
And if we're all gung-ho about giving abilities their full durations, let me introduce you to a little champion we like to call 'Morg'
We've also got full-duration Rumble Q
Soraka E (initial and root damage)
OMG Veigar W
Goddamn Viktor E (enhanced)
Xerath W (bulls-eye)
Yorick W (1/3rd less base, but 25% more scaling)
Ziggs E (5 or more detonations)
Zilean Q
And let's be clear:
These are ONLY champions labeled as 'mage'
Using ONLY one ability (others would have made the list if bonus damage that requires other abilities or AAs had been factored in)
counting only abilities that are AoE (single-target abilities tend to deal more damage than AoE abilities)
counting only abilities that scale primarily on AP (for ease of comparison)
Yes, MF's E is capable of dealing significant damage if she builds AP.
No, that damage is not extraordinary or unreasonable.
It is applied over 2 seconds, has a cast time and a delay before it is applied, and leaving the AoE stops the damage. It has plenty of counterplay.
'Mage Fortune' does not have unreasonable damage (be that DPS, Burst, or a combination of the two) either compared to other 'mages' or to MF's more standard AD build.