User blog comment:Kagiretz/Champions Powers, Advantages and Disadvantages ( Nerfs )/@comment-10540150-20140224011039

What you have to undrstand about Fiddlesticks is he excels against AD champs. And pretty much nothing else. Hard CC of any kind ruins his combo and leaves him helpless. He doesn't begin to destroy this form of counterplay until later levels when he begins to max his Q, and even then the nerfs did leave him less powerful in that respect. Don't get me wrong, I mained him for six months because I thought he was the most OP champ in the game, but then I started going up against people who understand how to fight him and realized he's really not that powerful. His scalings are there because he only has two sources of large damage that can be used in every situation, these being his W and ult. As I said, any form of hard CC will interrupt his W, leaving him without his main damaging ability, whereas he has to channel his ult from the brush for the same reason. Fiddlesticks relies on constant good positioning and, in some cases, his foes just plain messing up.

TL;DR Mages are restricted by their cooldowns more than pretty much any other class in the game. Fiddlesticks is even more restricted by this because the combo that he will use fifty percent of the time consists of only two spells, one of which has to channel for the entire duration in order to deal enough damage to make up for his lack of burst. Take away this combo, and he has no choice but to run since he has nothing to throw at you except a silence.