Ride quality is almost impossible to measure unless you only ask one person. We all have a different perception of "ride quality." Comparing lift to lift yields skewed results without a constant, ie the OEM ride of a Sahara (which can be used as a baseline feel.)
I totally agree that ride quality IS 100% subjective but, it is totally possible to determine what a "firm" ride is vs. a "soft" ride. Of course, one person may prefer one over the other but, that doesn't change the facts.
As for dualrate vs single rate, a dual rate doesn't HAVE to have inferior road feel than a single rate.
You're right, it doesn't. But, the people who tend to buy dual rate coils typically do so because they like to load up their Jeep to the point where the softer rate is used up and they end up just riding on the firm side.
If you look at that coil pic of the Metalcloak spring, you can see the large portion of the spring is the road rate (the stiffer rate) and a small section is the soft rate for offroad use and flex.
To be clear, the small section is NEVER used. Sure, it'll extend when at a full droop but aside from that, it does NOTHING. Contrary to what MC will try and sell people on, there is more to good flex than a lot of droop.
Now, on the road (unless you are slamming NYC quality potholes) you generally are not compressing the "stiffer rate" section of the spring to where the coils touch. Same goes on a single rate coil....you wouldn't compress the entire thing on the road anywhere but the craziest potholes.
Actually, if you were to compress an entire coil, it will have gone "solid" and that is a bad thing. If you do that even when hitting the biggest pothole or flexed out, you will have over-compressed your coil. In other words, you will have compressed it to the point where it does not return to its original height. This is the primary reason why you need to install bump stop extensions and at a height that is relatively equal to the amount of lift you just installed.
The flex rate coils are dormant and are generally not used on the road (unless again, you slam a pothole or something.)
According to the diagram, the "flex rate" coils are NEVER used, they simply extend when your axle is drooped out enough. To suggest they get used would mean that they actually do something to offer a better ride.
Now, I will agree with Eddie that dual rate coils are more complex and harder to get right.
The thing is, you can never get it right for everyone as everyone has a different idea of what right is.
Most of the time (not saying this about MC, I have no experience with them) suspension companies do things to just fit and that's it. There isn't real engineering behind them.
But, to get a coil to provide a specific amount of lift does take engineering. You need to account for weight of the vehicle, thickness of the wire to make the coil and how many winds you'll need to get you to the desired height. Depending on these factors, you will get different results.
A dual rate coil *could* be fantastic, provided it was properly engineered.
But they do make one and it's called a "coil over". Just because they incorporate a shock through the middle of them doesn't mean they don't have 2 different coils with 2 different spring rates of your choice. The real benefit of them is that they use much longer coils for both and allow you to set the timing on them so that you can determine when the heavier coil kicks in.
