A couple of things to address here! Your Mountaineer II will not have become dull from going in and out of the sheath. The cutting edges of our knives are polished - they feel smoothe, which is often misinterprested as a dull edge. The gusset of the sheath is leather - the blade is considerably harder than leather and it will make its own space in the gusset. The security of the knife in the sheath depends upon the rigidity achieved by knife resting snugly in the gusset.
I hope this helps your understanding - I don't believe there is actually a problem but if it continues to concern you, please be sure to send both knife and sheath back to us so we can check it out!
Anne