Are they all the correct pressures? Something's out of adjustment to have that type of uneven wear. Was the car new? Not sure about checking the balancing as you would notice if they were out as you drive but agree re alignment, needs to be 4 wheel. Despite your Dealer saying you must have hit a kerb ( or other spurious excuse) I'd go back to them if you have had the car from new, all pressures are correct and you know you have not gone 'off-road'.
If the car is second hand one might think one of the fronts has been swapped to the back but even then there still some variation. My last car was notorious for scrubbing off the fronts due to the aggressive OEM set-up but even so you would not get the variations you have.
Other possible explanation if second -hand could be accident damage, chassis out of alignment and not jigged back correctly...(worst case scenario I know!)