I find the coil works very well for the Ransom. The DHX2 seems to have excellent support when climbing and descending with the fox recommended settings. You could use a progressive spring if this was a concern. I have found the standard linear spring is excellent. It was a custom setup of a fox metric shock, but not specifically tuned to the ransom. It is definitely not wallowy with standard tuning suggestions and with the DHX2 you can add more low speed compression. Also, you can increase the high speed compression if you are blowing through the travel. I have not had either of these issues. I did try a 425 spring and did find this too soft for 198lb.
If you are constantly tinkering the downside is that standard tools will not work without taking the shock out to adjust the compression settings. I have considered making a shorter Allen key to fix this, but have not tried it.
I am not an engineer, but the feel of the leverage curve seems to have a progressive nature and with a 30% sag, I am not having problems with hard bottom outs whilst jumping or descending downhill tracks. Anecdotally, I found with the standard shock, I was using much lower pressures to achieve full travel than my Reign, which used the same size air shock. This suggests some progression.
I think the main benefit of the coil is that once you find the right spring rate you can almost set and forget and just ride the bike. No more worrying about spacers, air pressure, altitude and air seals.
Is it better than the standard shock? It is heavier, but I think for the reasons above better.
I think it removes a lot of variables and lets you just concentrate on riding. The traction and simplicity once set up are significant benefits.