This shows a more appropriate three-stage exhumation history, with a period of rapid exhumation around 20 Ma sandwiched between periods of slower unroofing.
Exhumation is purely by erosion.
The form of the cooling curve is now correct, but these models cannot exactly fit the T-time curve if the conditions of granite emplacement at 20.8 Ma are required to be in the kyanite stability field, because the fall in temperature is delayed too long to match the muscovite cooling ages.