Grass is a safe and forgiving surface
This is not a factually true statement. No matter how perfect the grass surface is it presents a greater chance of a rollover compared to pavement.
and is at least a better representation of what you might have to deal with in the real case.
No argument there. But, still a gas/petrol station parking lot, or roadway, or any number of other examples are probably better representations. How much risk do you want to bite off on in training? You are one of the most risk adverse people I know (on the internet).
If you let people only demonstrate their skill on a surface which lets you get away with sloppy heading control you are ticking a training box rather than keeping up to a standard (sadly something all too common nowadays).
Only if you let them get away with it. You seem to be implying that all instructors, or perhaps even most instructors, will become lazy and will not grade the student appropriately. That has not been the case in my admittedly limited experience.
The fact that instructors and inspectors struggle is exactly what I mean by dumbing down training.
I've not observed any instructors struggling. I have observed a single DPE who struggled. But this is more of a Robinson issue than a dumbing-down issue.
The widespread use of Robinsons and their lack of suitability as a training machine (due to number of accidents) has driven down training standards in the industry as a whole - well done Frank!
Look on the bright side. As Robbie alluded to, there really is some truth to the aphorism "If you can fly a Robinson you can fly anything." When I was over in your neck of the woods a few years ago and made it a point to get a couple of hours in the G2, on the first auto I literally started to giggle. It was so ridiculously easy! And slow. With piles of energy in that rotor in all phases of the auto. So I do appreciate the differences even through just that one example.
Bash the machine all you want. It's made rotary wing flight, personal and business, possible for many thousands of people. In the US the helicopter industry would be horribly maimed if they should all suddenly go away. I, personally, would not be flying helicopters if Robinson did not exist. It's a risk/reward tradeoff I'm willing to make, and I invest a lot of time, energy and money making sure I get the best training possible in order to manage the limitations of the machine.