As a Syndra main before since this years spring all i can say to this is that she might be able to delete most champs, but if you get at least some mr or go somewhat tanky, late game she tickles you with her ult, lol xc
I think shes fine, shes sorta like a lux bus has less range and follows the same princible, lands her q+e and you're most likely dead, same goes for lux, lands q does combo and you're either dead or less than half hp.
If you wanna counter her, just wait for her to waste/miss her e and then jump on her face, she wont be able to do anything. Of course a good Syndra wont just waste her e on the minions during lanning.
In short:
Syndra is like Lux but her ult doesnt have such long range.
Playing against her, treat her like Lux, misses/wastes her e and you go balls to the walls on her. (Also Zhonyas RUINS her :I )!!!
Dont let her hit her Q+E+W+R combo on you later on the game because that might be fatal, same as Lux E+Q+R xc