I tried setting up iOS devices a few years ago, and given up for the time being. I just couldn't work it out and blamed Apple/iOS, being the weird devices they are. 😛 In the past months I've set up a bunch of Android phones as managed devices and learned a lot. I'm about to revisit iOS devices.
With Android devices everything is tied to the user. Once a managed user logs into the device it shows as either user owned or company owned in GW. If you have an existing (installed and working) Android device and add the user via settings, it becomes a BYOD device and you end up with a personal and work profile. Interesting side note: you can push apps on BYOD devices as well, but if you try to install a launcher (like I did) you can't make that the default launcher. Logic suggests this is because the work profile can be paused (temporarily disabled), which makes the work apps unavailable, which wouldn't be a good thing for launchers. So any installed apps on a work profile cannot be made default apps.
However, if you factory reset an Android device and add the user while going through the initial set up, it becomes a company owned device, and there are no personal/work profiles anymore, just the company (work) profile with whatever settings were defined in GW. In this case pushed apps can be made default apps, including launchers.
I suspect this will work the same for iOS (will be finding out soonish), when you factory reset the device and during the set up log in with the user account, it will become a company device and you can contorl it like with Android devices. Well, within Apple's limits of course. 😠