Daz WRX

Engine light came on one Friday so took car to closest dealer for a diagnostics. Car was returned with reset ECU and sent on my way, car feels very slow now like no boost. Have a service booked in at another dealer so take it in and mention the history. Dealer checkes ECU but nothing there and resets again informing me that after an ECU reset the car will feel slower and advised to drive it hard.
I try this out but still feels the same, booked in again and what do you know the bloody wastegate was stuck open, now this is obviously completely fcuked now and me driving it around probably didnt help things either. Turbo damage now who knows but warranty claim now in progress.

Why couldnt the original dealer identify this problem from the ECU codes?

Rant over
Daz