When people talk about app store moderation, they're talking about a moderation team deciding which apps are abusive and which ones aren't. They're not talking about the underlying mechanism of, "there's a system that verifies an app doesn't violate its manifest."
The relevant part of the app store that people in this thread are talking about are the decisions about, "should a specific app that asks for location permissions be allowed on the store?" Code signing doesn't have anything to do with that decision. It's an implementation detail. The important part is not "Facebook is signed to a specific manifest", it's "Facebook's app will be rejected if it's submitted with a manifest that asks for privileges that aren't consumer-friendly."
The decision about which apps are allowed on the store is the part of the App Store that's relevant. When people question whether or not app stores improve security, what they're asking is, "does a centralized malware filter improve security?"
You could have a Gatekeeper model that worked the exact same way as Android, where the Manifest was required and the user confirmed the Manifest. Even in that world, Apple's sandboxing would still be better than Android's, because the capabilities Apple offers in the manifest are more intelligently split up, and can be granted in more limited degrees.
The question is whether Apple's security stats are due to moderation, or largely due to having a better set of permissions. I strongly maintain that there is not enough clear data for anyone to claim that the moderation is objectively the main contributor to those stats.
And that's really the only claim that djsumdog was ever making -- that it's questionable whether every company adding an app store to every platform is actually going to make most people safer.