That piece for me is done. Your casing formula is just fine. I agree with Whinewine, many things case mess with your leather. Cut out another piece, as well as, a piece of scrap from the same hide. Case and practice with your swivel knife on the scrap before you begin to get a feel for your project piece. As for how the swivel knife behaves? Your knife if sharpen and polished correctly will cut the leather (if cased correctly) like butter. If you think about that process there shouldn't be any drag. Consider how ABS brakes work on a vehicle.......that kind of travel is not good. Also, if you closely inspect the swivel knife cuts, ripples will show where the dragging was occurring.
Finally, your cuts should go down about 1/2 way the thickness of your project leather even if your piece is thin.
Good luck, sorry to give you some bad news about your piece.