Your first point is the reason SLS is a good feature, standard springs which is what I have on mine aren't a patch on Air so I imagine HD springs are almost unbearable without any load on them, but being that you've lived with them so long it's the norm.
The D3 is an improvement again the ride and handling is sublime, if you drive a D3 or indeed any 4x4 like a sports car you will tip it over,. Whilst the ACE uses gravitational sensors at high and low points and a hydraulic pump via valves and actuators to level the vehicle on turns, the D3 uses a computer to monitor the loads on individual air bags and adjusts the suspension accordingly. Similar effect but different method both effective
My first point is why I went for heavy duty springs, they can take the extra compression and then become less harsh, ask any HGV driver, or at least one who used to drive HGVs back in the days before more sophisticated suspensions and they will tell you that the tractor unit becomes more comfortable with the load on it.
As far as my D1 is concerned I started with it in standard suspension format, it was ok except it rolled a lot, I took advice fitted the Gaz shocks and roll was far, far less. I then fitted the HDs to the rear and the rears to the front (perhaps should have mentioned this) as I was going to start the long distance towing. It was and still is more comfortable than my D2.
The D3 in question belonged to a mate who drove me and Wifey around around in it, together with his wife and kids on roads near us in France that are twisty A-roads, but at normal speeds, i.e. not showing off anything at all. We hadn't noticed this nausea inducing thing when he drove us around back in England where we all live, just in France. He sure as heck wasn't driving it like a sports car.
It is worth pointing out that I have a bit of a lower spine back problem and Wifey has a titanium cage in her back and takes huge amounts of pain killers i.e. morphine sulphate etc, so there is no way whatsoever she could take it if our cars were not comfortable for her.
Sorry if this goes against the grain of your thoughts that the later suspension systems must, de facto, be better. Theoretically they may be, but in practicality we find what we have suits us and i am very happy I don't have to worry about an airbag springing a leak at an inopportune moment. the only experience i have of that is when an LZ member (Dutch) had this happen to him in another part of France and he called on me to help him out in a three way conversation to get him recovered from a slight off road situation, a ditch beside a forest track, where he was stuck, and then to sort out the garage getting the part (new bag) and fitting it. It took a truck and another 4x4 with at least one winch to get him out.
As an ex- MSA recovery crew member, i know that this would not have happened to him if he had not had air. Although I am fully aware that this is not the issue we are fundamentally discussing here.
As I said in my very first post on this thread, each to his own, you pays your money and you takes your choice, but there will always be moe than one opinion on stuff. You may think i am wrong, fine that is your choice. I just know that what I have suits me and i would not change it.
no one yet has mentioned 7-seater as opposed to 5-seater. Mine is a 5-seater and maybe that is a large part of why I don't have air and am happy with it.