You can see break pads without taking the tire off, have you ever looked at them yourself? It may require little bending to get the right angle and probably flashlight, not that I wouldn't trust the dealer but I would want to look at them myself, if it was my car. At 21k the wear is excessive but not impossible to get: Either you drive in a spirited way or something is dragging the breaks. Was the squeeling caused by the wear indicators? Regenerative breaking helps with pads wear but it has limited stopping capability and if you're hitting the breaks hard they will wear out almost as fast as in any other car. It would be very interesting to see how much front pads are worn out. If the fronts are above 60-70% then I would look for problem, if they're bellow 50 % I would look at the driving style.