I have a Specialized saddle and use with a thin “specialized pad.” I use the ultrathineline with it.
I made a minor change and used a HAF pad and my horse’s back was extremely sore for several weeks. I am not sure if it was not using the thinline or the change to the HAF.
I have a Christ wool pad too, and a skito. (I’ve tried them all) And I keep going back to the thinline with the thinpad. I have always taken the shims out of all of them.
I started using my Desoto saddle more and along with the thin specialized pad, thinking it was a saddle fit proble (made adjustments to the saddle also, but just wanted to test to see if it was the saddle)
If your saddle fits, I do not think it necessary to have a thick pad, it alters the fit of your saddle. At least it did in my horse and I am suffering (horse too) with a sore back that I am having difficulties resolving. I missed my last endurance ride and probably the upcoming one w/ his back.
Edited to add: One horse is a 1/2 arab/ saddlebred / dutch harness horse and the other a purebred polish arab.