I disagree that any of the modern iPads would run macOS just fine.
A system is significantly more than just its chip, and macOS is significantly more power hungry than iPadOS.
iPads have significantly smaller batteries, and significantly smaller thermal envelopes than even the smallest of MacBooks, anything that isn’t just the desktopwould likely cause any modern iPad to heat up and drain in minutes.
macOS is designed to gobble up as much ram and system resources as possible, iPadOS functions the exact opposite.
iPadOS keeps background tasks to a complete minimum, basically optimizing performance and efficiency at every turn. That’s how the iPad can get 10 hours of usage or several days with standby, despite having a battery that’s about 1/3 the WH of an MBP.
For reference, the latest iPad Pro has a 31.5 WH battery and gets an advertised 10 hours of Web browsing, while the latest MacBook Pro 14 inch has a 72.4 WH battery and gets an advertised 16 hours of Web browsing.
You would think with a battery over 2X the size you would get somewhere close to 2X the screen on time, but because of macOS that just is not the case. Do anything more power intensive, and the differences become even wider.
Spend just a couple hours running Discord, Mail, iMessage, Safari and Music on a Mac and you can easily drain the battery in 3 to 4 hours, do the same thing on an iPad and you’re still sticking somewhere around that 7 to 10 hour mark because of the power management of the two different operating systems.
Believe me, as someone who frequently has the conundrum of “do I really need an iPad?” Or “do I really need a Mac?” I have always wanted the best of both worlds combined into one device, but I think Apple has a point here that goes way beyond input methods and is down to a fundamental OS level.
macOS on the iPad would likely technically work, but it would be a significantly “worse” experience. Worst battery, worse performance, worse optimization.
For an example of what I am talking about in action, open a whole bunch of apps in window mode on the iPad. Once you reach eight or so apps open at once, the iPad will just, start force quitting apps to allow for new ones to be opened. macOS would not do that, it will slow down and start beachballing before it forces an app closed.