I just got some Prestige ones and they are not THAT thin. Adequate, I'd say.
In all honesty, if you want THIN you have to sacrifice sturdy. For my new saddle with VERY TIGHT stirrup bars I just bought an inexpensive pair of single-ply leather ones. Very thin, but I know they're going to stretch and probably won't last 2 years. It's a dressage saddle so I don't really care if a leather breaks.
I *love* these but the "tip" of the leather has 2 layers of material on it to make it more stiff, and this botches up the "I need something to slip under a tight stirrup bar" plan. However, other than that these leathers are GREAT--very soft, supple, don't rub the leather, and very hard-wearing.
I love my Prestige leathers. First pair lasted 6 years of very regular riding. Now I am onto my 2nd pair. Other companies make calf skin leathers that look similar for less money (like M Toulouse) but they tend to not hold up as well.
I love my webbers. I have the orginal and the leather kind. Much perfer the original. After almost 20 yrs of riding in them I abosulely hate regular leathers. Even "thin" ones I can feel the lump. I will never go back to regular leathers.