Fidd KSes adc with ult...

Thresh is tanky, has better CC and an AoE shield.

Both better in their own ways so just depends on what you need. If bottom has a tank and adc then I'd go for thresh because he less squishy. If there is no tank then I'd more likely take fiddle. I do think fiddle has better moves. Fear and silence..if he had a heal for the adc he'd be the best support.

People that say thresh's damage or CC in a teamfight is lackluster are building him too supporty. He is a blitzcrank wannabe, you have to build him like blitzcrank. That means no gold per 10 (except runes), just build manamune and tank items, and not only will you do halfway decent damage, you'll end up a REAL tank, and your long cooldowns won't matter too much because you'll survive to drop another set of spells before the fight ends, and you can lay out ranged muramana damage.

Because Thresh can actually build support items and be useful instead of half assing AP items to end the game as a half assed AP that does moderate damage? Because Thresh has more than 1 support button? Because most of Thresh's CC isn't reduced by merc treads? Because Thresh already has a brain?

He probably has someone's spleen and liver too, dude's creepy.

No teamfight presence, what? First of all, Skarner ult + lantern = even more lulz than blitz pull + lantern. More seriously, has anyone thought of the fact that he can pull a disruptor like Ali to the back line by pulling himself while leaving his lantern on his allies? Second of all, he has a Naut-level pull that doubles as a stun while not putting him at risk. His e kinda works as a mini stun also. Thirdly, his innate on-hit makes attack speed bruising possible similarly to how Irelia does it, except wits end + malady or wits end + runaan's something instead of something sheen related. I don't care who you are, getting hit for 300 every 3/4s second hurts (assuming 125 souls or something like that, you get 125 + (25 + 10% ap from malady, which should be 15-21.5, 21.5 if you get abyssal scepter) + 42 from wits end + base 85.6 ad at 18. If you get abyssal scepter and sorc boots both, you have 15 flat magic pen and 48 mr shred, resulting in a flat 63 mr you ignore. HUGE. If you choose to go tanky bruiser, you can get merc treads for more mr and tenacity, I would still probably get abyssal scepter since only possibly runic bulwark would be better for him defensively (you just benefit the team better defensively with it, really), and you can build either warmogs (since you get soul armor) or either randuin's omen (hp, armor, and cc ftw) or frozen heart. 1 item leftover, if I've kept count right.

My rant is WAY out of place in a support thread (since it assumes a non-support build), but I still felt the need to comment on the whole no teamfight presence thing.

Well, you see OP, Fiddle's role isn't technically a support. So theoretically, Thresh should be a better support.

Yes, his ult needs to be reworked, whether that be reduce the CD, prolong the slow, change it to a stun, such as Veigar's Event Horizon. I honestly would rather have Event Horizon, than Death Sentence. Cast from a distance, 2 sec stun..
But his grab is ridiculous, if you play him right, you can lock someone down for 2-2.5 secs before they can move with an E follow up. Thresh's kit is fine. Just his ult CD is WAY too long.
Taric's ult is under a minute, AoE damage, and AD and AP boosts to all surrounding champs.
Lulu's ult is 80 secs, gives bonus health, knocks up nearby enemy champs, and slows them.
Thresh's ult, 160 secs, slows enemy champs IF they break a wall, then the CC after that first wall is useless, much less the damage.
I love his passive, I love his grab, his knock up is meh, but I can live with it, and lantern is very versatile. Ult just needs to be reworked IMO.