Realistically speaking, why is that relevant? Like, if you're in a situation where you have to actively stop three people at once, the point of failure is a lot earlier than that. I mean, yes, she's bad in these situations where her lack of a mobility spell really hurts her but, at the same time, that's also a scenario that you would actively avoid even if you had one.
Jinx's strength is how fast she can convert a bad situation to a worse one for people caught against her. Conversely, she has little to do once she's already in a bad spot. Basically, she quickly goes from bad to worse on both ends of the spectrum.