Yes, the saddle is sitting downhill on the horse. You can see that from the first rivet, making a line to the concho on back. The line should be flat, not going down like it is.
Shimming is filling in the spots where the horse is lacking muscle and making the saddle level so that the horse can actually use his body. Shimming DOES help. Then, once the horse starts building muscle, you change the shim pattern accordingly. It's difficult to do that, however, unless you have an awesome saddle pad like this: www.ridinghighllc.com