One thing to consider: Seeing a NM whip to an under residential sink disposal as needing physical protection is not a 100% uniform opinion among all local AHJs, even today.
OK you are correct that 100% of electrical inspectors and even home inspectors will not write up NM running to the disposal. I agree with that. But some will and I have no way of knowing who will be inspecting in the future.
What I can "guarantee" is that if I run this in greenfield that it will pass
all inspections and it doesn't matter who the inspector is because it will be protected and strapped so there is nothing for them to write up.
The same goes for a disconnect and greenfield at the water heater.
I give a warranty on all work and if a future home inspector can find fault with my work I will take care of the problem for free and that hasn't happened so far.
The most costly thing a homeowner can do is leave a house they are trying to sell on the market because next month is may be worth much less than today.
If the only thing standing in the way of a home sell is a little geenfield at the disposal and water heater it would be crazy to argue about it just so an electrician can say he is a little smarter than a home inspector.
We are not talking about real high dollar repairs here and the most important thing is to get the home sold. Sales is a confidence game and if people start to lose confidense in the home inspector and his report they may not buy the house so it's important not to make him look like an idiot (even if he is).
All I ever guarantee on one of these jobs is that I have taken care of all faults found during the home inspection process and that all items repaired are under warranty and this has worked so far. I brand the panel with a sticker and leave business cards for the inspector and new owner and this is how you get a foot in the door with the buyer.
The stuff you repaired is under warranty and all the items missed by the home inspector are not and that's the real goal here is to be the one called once they figure this out. The new owner looks at your work and it looks very professional and the rest of the place looks like crap. Who are they going to call?
Homeowners don't know anything about electrical codes and if they see the disposal is run in romex and they think it looks bad and the home inspectors doesn't like it that's all that counts for them. Their opinion does count, not legally but as consumers because they get to decide where to spend their money.