Currently, sharing security issues with Apple is a guaranteed that the tooling you are using to get access to your device won't work anymore, there's definitely an bad incentive to not report security flaws at the moment.
I take your point, which is that jailbreaking is good if what you want is to run random unapproved code on your machine. But you didn't seriously engage with the comment you rebutted, because it is also true that jailbreak prevention prevents persistent kernel compromise --- is in fact a predicate for preventing persistent kernel compromise --- which is a thing that really does happen; in fact, it's far more relevant to the overwhelming majority of Apple users than running unapproved code is.
To have an idea if an app is sharing your data you need to be jailbroken, to have an idea of what is being sent from your device you need to be jailbroken, to force a stricter control on apps you also need to be jailbroken. I mean, you get the point. Any action you could do regarding security requires you to be jailbroken first.