Forget iPad replacing macOS, at this point I’m fascinated by the idea that an iPhone Pro might actually run macOS-like in the future for developers. It’s been a decade since the first jailbreaks were commonly available and we could run shells and other background apps—at the expense of battery life. Apple has built everything they need to keep things safe even if they open the sandbox... they could treat it like location permissions and continuously prompt, allow only some apps, spy or sandbox what function calls apps can make by default, etc. Yes, it could be abused, but they could cloud-scan files before running, or even require signing and submission. I know folks will keep pushing for fewer restrictions, and I know the business reasons that keep Apple from doing this. But this use case won’t ever actually go away...

OP is just saying that deciding to do that has a usability and security cost that some users will perceive as a net negative.

I know it’s a toggle, but as soon as that toggle exists app developers will use it to provide unsigned copies of fortnite to the kids, it won’t just be for pro users.

This is the point of contention here, imo. Jailbreaking, sideloading, and turning on developer modes are not always informed decisions. I've personally serviced hundreds of iPhones that have had all these things done because someone followed a set of instructions without knowing what they were doing or had someone else turn the option on without informing them and then they were exposed.