Mid game she loses to virtually any ADC in a 1v1 or teamfight due to lack of any innate on demand AS/AD steroids which shines/at its strongest in the mid-game with Runaan/IE.
And just because I know this will be your first response, no, her headshot is not on demand. In a 1v1 she'll get maybe one or if she's lucky two headshot procs off in mid-game 1v1 which won't be doing that much damage, v.s. someone like Lucian, Vayne, Twitch, MF, Tristana, Ezreal, or Jinx.
You know, basically the entire ADC pool?
Teamfight, she may get more off but they won't be hitting like a cannonball at this point. Not only that, her seige potentially at only 2-3 items leaves a lot to be desired.
The problem with Cait that makes her appear so strong is the fact that its difficult to gauge when mid-game is happening, because her mid-game IS pretty pathetic, her base damage on all her abilities are pretty abysmal, she doesn't have enough damage items just yet to hold out on her own, and she's not quite strong enough to seige at the mid-game. And she has no steroids to hide said weaknesses.
She effectively can't do anything at mid-game if she's not fed, but people don't understand how to abuse it. Or she'll get fed early game which then translates into completely by-passing her weak mid-game point.
In order to curb her frustration, they need to shift her power budget to make her stronger in mid-game and weaker in either early/late, as it stands right now, its difficult to gauge her low point and punish her for it.
The way I see it, I'd rather see her late game power shifted to mid-game, being able to stack her traps the way she can in seiging at late game is just bull shit IMO, you can play around it for sure, doesn't make it less irritating however.
Or take the headshot ability off of her E, its a mobility spell and it slows, that's enough utility for it to make a massive impact that it does not need such a large offensive capability in late game.
Or take the opposite route and power her into a hyper carry seiging ADC dream and make her early game weaker. Though I don't think this is the right route as one reason why she's powerful early is due to her 650 attack range which you can't really mess around with outside of gutting her base stats.