DFG wasn't a core item on Syndra and only situationally better than Deathcap. It's active was effectively another Dark Sphere in her rotation, at the sacrifice of a Dark Sphere ... so her ult burst only marginally improved, at the sacrifice of damage everywhere else.
Anyway, her Q most likely needs its damage back. She has no early trading power against any sustain pattern, and all meta picks have means of sitting back and 'out poking' from distance. Her all-in nuke around 6 is still the same, so I wouldn't say the full 20 damage. I'd be fine if her level 2 Q jumped up by 10 damage to avoid the 'level 2 kill spike' they got rid of in the first place.
Her passive actually needs to exist in a meaningful state. It activates too late to make up for her laning phase and it doesn't do enough to reinforce her team fighting. At the moment she has no team fighting synergy in her kit because she has no way of addressing the frontline. Using her ultimate on tanks is an awful strategic decision and almost never works out in her favor, so her high burst isn't 'good' for that. The sustained damage from the rest of her kit, however, is not enough to actually scare the frontline unless she's obscenely fed. Contrast to Cassiopeia, who can drill through pretty much anything in front of her at will.
I'm generally in the camp to give her passive more 'ramping damage' thematics, rather than burst, so she has two primary play patterns to work with.