Cait can't 1v1 any other ADC if they are on the same playing field is why. She is a goto ADC because of how easy and safe she is, its literally no different than Ezreal, he is a safe pick but generally won't compete with the riskier and more rewarding Adcs like say Ashe or Vayne which can be easily popped but if they do what they want to do, they can easily be the sole reason the enemy gets murdered.
Runaans helps her headshots more sure but they alone won't save her if she can't get multiple of them, she relies on doing her net, Q, auto combo to truly deal damage, and its easy to dodge that net, her Q is easily sidestepped, and it has reduced damage as it hits things prior unlike say Varus Q which even if it hits the entire minion wave will still take a big chunk out of you. Traps yes she can make great use of them from CC but if there is no cc, don't walk into them, its not hard to imagine where she will put them. She will place them around your tower which you just simply get rid of when she goes away, or in bushes which you just be careful going into them at the very tips.
She can't burst you, she doesn't really have CC since her traps are only work if you are prior cced. And her ult is nearly worthless since it can be blocked, often being used to start a fight then end it since it will never get the kill you are aiming for.
In return she is extremely safe, she can do high damage if you let her get multiple headshots in a row, but give me Ashe over her any day. I would rather feel useful to my team or be able to do something myself than 100% rely on my team.
