Both of these characters are missing combat abilities so the abilities they do have are stronger than other characters. That is the main issue with both of their design but not necessarily a bad thing.
Both are also duelist. They are designed to be able to fight 1 to 2 people at a time and come out on top but have minimal team fight presence. Late game Mirage turns into a long range debuffer usually (also support and drain tank are pretty good) while cali turns into a beefy body.
that being said, mirage has minimal mobility and if over extended can be easily killed, this is why most play long range.
Calico can be shut down with a 1750 active item. that is super cheap and easy for 2 people to buy to shut her down mid fight and kill her if her team doesnt save her.
Imagine how much more pissed off if the only way to stop her is you have to buy knocked down like you do for several other characters. Or worse, curse.
