Are antivirus and security apps on mobile phones actually worth anything?

Not talking about enterprise scale, but for personal use. As a professional in the field I often get asked this, but I really don't know what to answer, other than that personally I don't even use them. While I don't see exactly any harm in them, I also don't see much use for them either, as if you're going out of your way to download and run third party apps and granting them permissions, no security app is going to save you. And if a malicious app is downloaded from the legitimate app store, good chance it's either not getting caught anyways, or it gets caught by the appstores/phone manufacturers own av software.

I guess same question could be extended for pc's as well. Since win10, I don't see much benefit in using something else on top of Defender. Am I dead wrong?