Her early game is bad and this meta games end before she can scale up. Ezreal is strong and will poke the shit out of her and blink over her chompers. Zed is her worst nightmare and he got buffed. She gets destroyed in ganks and fewer wards means she can't avoid them. Her rockets fire rate got adjusted and now are worse early game. Tahm has godlike synergy with her but he got nerfed and was banned every game anyway. She feels fine right now in low elo but thats because people dont know how to bully her (of course you're a hardcore Jinx main so your experience is better than many non-ADC mains who just play her because she is a safe pick and easy). Might as well play Vayne who at least can safely solo farm lane while her support roams mid and gets the game snowballed.
Jinx is my favorite ADC but for now I just pick Quinn, stronger early game, fast roams to snowball games, resistant to assassination, can take care of herself and doesn't need to be babysat all game.