I can't imagine trying to do that on an iPhone. Surely it's useless.
What this does do is reveal the fiction that "iPadOS" and "iOS" are separate. Clearly not.
Just as a N=1, I would rather pay a recurring fee in the Disney-Netflix range to Apple to get more liberty in usage from my machines. But I think they don’t dare to go those routes, because they need the broad market base and cannot extract the current cash flow from a smaller base, while setting expectations that the Googles, Samsungs can copy.
Industry leaders dilemma. Apple currently settles on market differentiation via physical products.
Only for the truly low end. The thermals alone are a serious difference, you can't expect an iPad-class device to support the same power dissipation as a legit MacBook.
They're not doing it today because current Apple leadership doesn't have the same incisiveness as the one back when they were sacrificing their most successful product on the iPhone altar so the competition can't. And to be fair, Apple has a much stronger position with a wider moat then they did back then. So they can afford to give more time to the competition to compete.
Apple wouldn't just sacrifice the entry-level MacBook product category and I'm not even sure about that - the look-and-feel of a "display with attached keyboard" (i.e. Thinkpax X1 Tablet-style) is vastly different from a bottom-heavy Macbook with actual hinges. The former isn't really usable as a literal laptop unless you got some seriously long upper legs.
The more important thing that Apple would have to sacrifice is the App Store cash cow and users not having root rights. On a iPad or iPhone I'm willing to accept that, but on a machine I actually want to do work? No way in hell.
But that's it right here. It just takes boiling the frog slowly enough. The high powered M-powered iPads are already testing the waters of what people will accept for work (I don't think they're aimed purely at content consumption like the "smaller" iPads). I think Apple can afford to wait because they don't need to cannibalize anything today, and because the replacement isn't strictly a superset of what it's replacing, it comes with the caveats you mention. As soon as the market is ready to tolerate more lock-in, it might happen.
Enough people do just emails/Teams/Office for work so plugging in an iPhone and turning it into a desktop with mouse, keyboard, and external screen(s) can tick all the boxes for usability. Or an iPad with keyboard since similar sized devices were historically used for portability. Most work devices are locked down anyway, no root, no software installation.