bad comparison - here is one better, not a perfect one...
You can't enter a car into a boating competition. The question here is: if you take basic precautions to make it the same class of boat - a modified car turned into a boat should be a valid entry - provided the engine speed roughly matches.
People worry about cars on water here, not knowing that doesn't exist by definition: any car in water has been modified from a car to be a boat. you may recognize that it was once a car - but that's vestigial shell stuff. the inter-workings are a propeller - not a wheel.
I see your argument and has some merit but isn't persuasive enough. I would posit that its a bit too loose and that it breaks down on biological people have many more complicated systems that aren't simply re-categorized similar to your car and boat comparison.
For better or worse nor is our medical science sophisticated enough to swap out the systems to be true comparables (and I don't mean to offend anyone).