Please explain the difference and I will in detail tell you how each point you make is incorrect.
Phones are generally always on and always connected (network, cellular connections, bluetooth). Laptops and Desktops are generally connected to a local LAN (yes laptops have cellular connections too), but not "all" the time. And generally behind a firewall of some kind.
Phones have smaller batteries and historically had far less processing power compared to a desktop/laptop computer. You had to run a "lesser" OS vs a desktop as to not over utilize it's limited resources. We spent years maximizing our battery life on these devices so that it can last you as long as possible. Vs a full desktop that can draw as much power from an outlet as it needs. Or a laptop that has a larger battery, and can also draw from an outlet.
iOS and it's devices were also designed with touch/multi-touch in mind. So the whole OS was made to maximize that type of user input. macOS was not, as it's designed with keyboard and mouse input. Yes, you can make it work with a touch screen. But, it's UI isn't well designed for it as it is for iOS/iPadOS.
Printing. You have AirPrint on iOS, so the printers drivers are not loading up space on your device.
Apple has limited iOS to what it needs to function "best". All desktop features are not also in iOS, as it's simply not needed. Would take up more storage space. Another thing these devices don't have as much of (space and size of the devices are smaller). Yes, they have 1TB of space on these things now, but that's "now". It was designed with the hardware of the time. Kind of like why we don't see a whole host of handheld devices running full Windows desktop OS. It would kill the battery, and require a more power hungry CPU/GPU/RAM/ and on and on. Yes, you could do it, but it would be like one of those handheld gaming devices.
iOS limits the ways in which you can install software because allowing it via any and all means such as a desktop computer would increase the attack surface of the device/OS. Originally, iOS was not going to allow 3rd party apps. Yes that changed (clearly), but they compromised. Limit the way in which apps could be installed, and a means in which to secure those apps as made by as many trusted sources as possible. Something that is NOT possible to do on a desktop OS. It wasn't built in the same way, and we are all very used to it being more open. However, I don't enjoy all the pop-ups for security access on my macOS to allow this and accept that. This is practically non-existent on iOS. It's a trade off, and one that in many peoples view makes more sense to keep it that way because it's inherently more secure than to make it wide open like a desktop. Could we make them more similar? Sure. But at what cost? What's the trade off's? What are we truly gaining by allowing this? And more importantly it will not happen overnight.
How would you provide at least the same level of security as we have on iOS today. While also allowing a 3rd party store and side loading apps? Just by allowing that to be possible increases your attack surface, as these are more ways into a device than it currently has. The company for which I work for only allows internet access via 1 location. Basically one way into and out of our organization. Everything gets monitored from that point. Smaller attack surface, and easier to see all the traffic going in and out. Vs it being from each location, and having to monitor each location independently. If something happens, one place to shut down the traffic. As you simply can't evade it.
Same for application deployment. Users are not allowed to install whatever they want. It's a security risk, not just because they could install something even if they needed it. But, so could a bad actor. Visit a bad website, and boom your done. Open a bad email, and boom your done. This is much harder to do on an iOS device. Where clicking a link is even easer than deleting it first.
This does lead it to being a one size fits all approach which doesn't work for everyone. But, it's the approach Apple wanted as was free to try. They could have failed in this approach very easily.
