Fiora stomped in soloQ but was bad against coordinated teams because she was completely selfish champion. Selfish champions work against randoms but not against coordinated teams. Fiddlesticks relies on the enemy team doing a poor job of keeping track of him and not counter-jungling, which is a pretty common thing in soloQ.
Both were champions that are heavily reliant on a lack of coordination but never see pro play mainly because they abuse the soloQ mindset.
Here's some explanations to his problems:
- E has 750 range, travels slowly and has extremely variable effectiveness depending on RNG
- E's silence simply isn't enough to do it's job since it lost the bounces
- Q and W have a range of 575, with the tether in W being 650. most gapclosers have a range of 600-700 and most untargeted dashes have a range of 300-425. Fiddlesticks just becomes a CC-bot without his ult
- Speaking of his ult, while iconic and powerful, far too much of his power budget is loaded into the base damage of it.
- He can't farm for shit, killing his ability to solo lane at all.
- Runeglaive is shit on him.
- There are some hard-counters that are just brutal for fiddle, one case being Olaf with his buffed ult. If Olaf can see you and he wants you, you will die.
- Disgustingly vulnerable to counterjungling
- ult is hard countered by wards
- He's one of the squishiest champions in the game period.
- His main damaging basic ability effectively requires him to CC himself. (Which wouldn't be so bad if it weren't for the squishy thing)
- His passive is borderline worthless.
And all of these shitty aspects about him a deliberately kept that way or are the result of nerfs. These are there to keep his SoloQ in check.