The leather in my 300E is very smooth grain, but very stiff, in spite of the fact that I keep it treated. I get the idea that it is very thick.
The leather in my '96 with Premium leather was much more supple with medium grain.
The leather in my '01 C Class with Premium leather is supple, but heavier grain.
I believe that much of the life of a leather interior is determined not only by the skin itself, but the seat construction.
Have a great day,