Her kit isn't "overtuned."
Her Q is nasty, but also centers around her being the ADC with the lowest base attack speed in the game and one of the shorter ranged ones with her base weapon (the minigun). The rockets take mana and aren't really long range until she has at least 3 levels in her Q.
Now her minigun has a fast attack speed if her Q is level 5, and she doesn't switch, but the instant she switches she starts losing attack speed, or if she just stops firing for more than a second or two.
Her W has a very easy to see aiming line and a long charge time, its rather easy to avoid.
Her chompers don't arm immediately making them easy to avoid.
Her Q only does max damage at range and is half damage until its about a screen width away from her.
Every item has some exploitable issue.
As others have said, early on Jinx is extremely vulnerable to burst damage, and she isn't a great duelist until she has Q to level 5 for the attack speed. She's one of the weaker early game ADCs if someone is willing to trade with her and force her onto the defensive. And ADCs all have weak early games compared to most other champs.
Jinx also is horrible if she's behind. Which is how you defeat her. Gank early, gank often and make sure she doesn't get farmed up. If she's 1-2 items behind most of your team, she's not going to be able to do damage quickly and you can just focus her down in teamfights.
It sounds like you fear her abilities too much to see the ways to exploit her lack of mobility and slower than average attack speed. I've had games where I run into people like you and Jinx dominates the game. I've also had games where the team facing Jinx went in hard to bully her early and made her completely ineffective for most of the game.
