Let's not get carried away...
I agree, the iPad is the future, and I think that now that Apple is dedicating time to it instead of bundling it with iPhone software-wise, we're going to see an upswing in sales. It really is all the computer most people need.
That said, macOS is still the best desktop OS there is, IMHO, at least today. It is WAY more powerful and efficient than iPadOS in many scenarios, and the hardware is too. Can't start getting rid of the trucks because we really, really like the cars now can we?
At the source, these OS are the same (according to Steve at least), so I believe convergence is inevitable at some point.
But I think Apple's approach is correct: Two OSes for two VERY different types of hardware.
As a MBP fanboi, my response would be:
If iPad is so much the future, then why have iPad sales steadily declined so much faster than the decline of laptops/desktops for years? (NB: laptops/desktops have been declining slightly because most home users who simply browse the internet and use email can now do that on a phone and don't need a full computer at home. All those that do real computer based work still have a computer. Sure, some now use an iPad instead, but not many in comparison, or at least not many that don't also have a computer too). Nah, they're a toy for most people who need to do any power work. The only way to make them a real computer is to put a real OS in them, add a real keyboard and trackpad (as they have done), and put enough RAM and SSD in them to make them useable for multitasking and storage, so basically make them a MBP, and at similar prices, with the only distinguishable feature being a removable keyboard. Or take a MB and add a touch screen, with the only feature difference between a MB and iPad is the removable keyboard on the later. So be careful what you wish for, as to pull it off, the prices of iPads will have to go up.
The MBP is a sports car, not a truck. The iPad is a tricycle.
To converge iPadOS and macOS would require removing the walled garden. So if you are going to do that, you'd just take macOS and add touch screen capabilities to it. You wouldn't take iPadOS and add all the features that had been removed from macOS in the first place. So again, if you're going to merge iPad and MB, you're just making iPad a MB with removable keyboard. In your analogy, turning the car into a truck. In my analogy, turning the tricycle into a sports car You're never going to dumb down the MB into an iPad without simply losing all those customers to Windows (and not because they will want to, because they will have to).
As a mature human, my real response is:
Their seems to be a war going on between MB fanbois and iPad fanbois, with both wishing the other didn't exist and all converted to the promised land. Both sides are delusional. MB fanbois love the form factor and capabilities, the physical keyboard and trackpad are the essential, efficient tools for fast volume data input. iPad fanbois love the form factor, the touch screen is essential and efficient for the fast, efficient GUI navigation, and data input is low volume, so doesn't need a physical keyboard, and most data input is either tapping a selection, or art based drawing input. They are two completely different use cases, and both see their use case as the sports car. So let's all make peace, and realise the both should continue to exist, and neither knows what the other needs best.
Apple isn't stupid, both are $5B revenue streams on their own, and both add to the ecosystem that drives more iPhone sales. Neither are going to replace the other, and neither are going to die off. Apple are merely beefing up the capabilities of iPad, and in an optional way, so people who need the beef, can pay for it if they want, e.g. the new expensive keyboard. They are also trying to merge apps to a degree where you can use apps on both iPad and MB, but I'm not sure if they are aiming for 100% compatibility, or merely an overlap for the simpler apps.
