> The engineers who are most likely to be under-performers are also those who give super inflated estimates for simple tasks.

Definitely did not seen this. Under performers are underestimating or just do wild random guesses. Under performance is most likely to be in the form of "making small estimate, try to make it technically, but then it has about millions of problems".

Big estimates require courage and confidence - under performers usually do not have either. They are too scared to estimate high.