After looking for some considerable time into a new AP champion to buy, I mostly disregarded Syndra due to negative votes about her. However, I tried her in PBE and looked at her ability stats in comparion to the much loved: Ziggs...
If both champions end their build with 600 AP (typical of an APC), Zigg's Q never does over 50 more damage than Syndra's Q (at rank 5, Syndra's Q does more damage than Zigg's Q) whilst her Q has a constantly shorter CD until rank 5 and constantly costs less mana, Zigg's E in comparison to Syndra's W is much less reliable in terms of damage due to the fact that about 50% of the damage is easily avoided, and her W has a much shorter CD (I do understand Zigg's E can zone and set up choke points), Zigg's W loses on the exact same amount of damage to Syndra's E as she loses on her Q to his Q (so that puts the damage in Syndra's favor with her W), Syndra's E constantly has a shorter CD, has more reliable cc and has a built in stun if need be along with the knock back. Zigg's ult understandably does much more AOE damage with a much larger range. But Syndra's ult has FAR higher potential single-target damage and has a massive AOE stun to follow up with her E in teamfights, which Ziggs does not have. So, with that settled and proven that Syndra does more damage in a normal burst than Ziggs to a single target, why is Syndra so hated in the community?

cause to use effectively it does take some skill to play her and maximize her damage for her ult.

Because she's not easy of course.

Syndra is hard to play, and has .5 escape abilities. The knock back is not that great concerning every champion released seems to have a dash/blink. In order to stun she has to combo 2 moves together, which makes her mana hungry.

Too much micro managing in a fight for Syndra, and Ziggs passive makes his basic attack do extra dmg.

The reason people think her damage is lacking is because it was when she was released, but she got a buff THAT APPARENTLY EVERYONE ON THE PLANET DIDN'T SEE so they continue to hate on her.

It's seriously annoying when I try to play her and get dodged or trolled because idiots didn't pay attention to the patch notes.

She is alot better since the QOL changes

No pro players picked her in a tourney yet.
Got to wait for someone with a big name to do well with before any decent amount of other people also begin using her. . - .
I personally like her, the changes she got make her seem pretty viable, imo.