This is a false argument because even the first party offerings have security and privacy issues. Apple has redefined what "privacy" and "security" means to imply "only things we make" as a sort of selling point. Yes, they make OK things, but who is to say someone can't make something better? Cooler? Funkier?
Also, what happens when the entire planet is vulnerable to the same flaws? It's rhetorical - you get security companies offering services to unlock and decrypt devices for anyone willing to pay them. And what happens when Apple decides to say... remove XX category of apps by a government request? You end up with people owning very expensive slabs of glass and titanium because they weren't allowed to look for apps elsewhere. Apple's way is not the way.