I disagree, I think fiddle does exactly what he is meant to. He's a high risk very high reward champ, and because he jungles, and does so with about full HP the whole time, he is an AP-Jungle-Assassin, and he's a lot better at it than people think.
This is a list of mages that can kill multiple targets from a distance with their ult.
Fiddlesticks Ult Range: 800 and Base Armor 11 (+3.5)
Lux Ult Range: 3000 and Base Armor 8 (+4)
Ziggs Ult Range: 5300 and Base Armor 12 (+3.3) (not sure if that range is accurate?)
Anivia Ult Range: 615 and Base Armor 10.5 (+4)
Xerath Ult Range: 900/1300 and Base Armor 12.6 (+3.4)
Veigar Ult Range: 650 and Base Armor 12.25 (+3.75)
Rumble Ult Range: 1700 and Base Armor 16 (+3.5)
Karthus Ult Range: Everyone and Base Armor 11 (+3.5)
Kennen Ult Range: 550 and Base Armor 14 (+3.75)
There are a few more but whatever.. Kennen is the only mage besides Fiddle that is inside his own ult. He has higher base armor and overtime armor.
Anivia has a similar ult to Fiddle but she is not inside it. She has slightly better armor overtime.
Fiddlesticks armor should be around what Kennen has and fix his drain damage + passive.
He is the highest risk mage because of his ult. With the same reward as any of the mages above. To top things off he doesn't have stable damage. 3 of his abilities do damage. Dark Wind is random damage. To land Drain you need to be fairly close so you are bound to take some heat just trying to. His ult is great damage but easily countered besides the one person that you fear. Not saying you can't get multiple kills. Just saying that you won't if you are playing ranked with people that know how to play.