It is a very daunting problem no doubt, maybe the hardest one, but I also don't doubt that the end form of Starship will require way, way less than 20 000 man-hours per turnaround (as the Space Shuttle required) to refurbish the heat shield. They simply cannot afford that.

The way they are going they can try 5 different ones that fail until they find one that doesn't.

Contrast that to the Space Shuttle which required a human crew to flight test anything.