Yes, phone operating systems are more modern, and implement: sandboxing, hardware security, MAC, app permissions, etc. That’s why they do less. In this category, I would use iPadOS in lockdown mode.
But a phone is a device for the every day use of an average user. It’s not designed to be a security device to protect people against targeted attacks. If your threat model is a state actor, you might be better off with a desktop. Phones have phone numbers and take unauthenticated input from the external sources (messages). There is an opaque baseband chip. The threat model in which they are secure is skewed in favor of the phone provider: essentially you rent their device, and share your information. Phones communicate information about user such as the location, and might conveniently backup users data to the external servers by default. There is limited app choice. You can’t inspect, select and customize a phone OS. On the other hand, I can cherry pick a desktop OS, even build one selecting components, see, monitor and control the software, and run it on hardware from a source I trust.
No, we just don't agree. I've spent a fair bit of time on this problem, and more time than that talking to people who specialize professionally in helping targets of state attacks protect their comms, and the consensus I've heard is that nobody is better off on a desktop platform. If you're using a mainstream desktop/laptop platform, even Belize can afford to buy their way into your device.
I'm not saying this to convince you, just to establish that we are definitely talking about the same thing, and I am definitely not being flippant.
