Except the iPhone is really not on the users side. I do tend to think the iPhone isn't going to spy on me, or at least if it is, it's going to be doing so to a much lesser extent than Android.
But it's also not going to, for example, let me install a web browser which is anything other than a Safari reskin.
There are other factors to 'being on the users side' than just privacy.
Honestly Vulkan was just a lazy example, but it's hard to give a good one when I don't use Apple products in the first place.
A better example might be places where it's hard to switch away from Apple's systems, or perhaps how they only support hardware that doesn't last very long and are notoriously hostile to attempts to repair your device.
I couldn't agree with "people want a phone that is on their side" more.
I also agree that Linux matters as much as iOS's BSD heart—that is, it doesn't. But this is also why the Vulkan example doesn't serve your point. As with Linux, technical implementation details aren't why people are using iPhones.
Most people use iPhones because of the complete experience. For the few who care whether the iPhone is "on their side", it is clear that Apple's business model is generally aligned with their interests. This is either unknown or untrue for alternatives.
This is where open source phone vendors will fail. Trust is not simply a technology problem.