SpaceX knew that the concrete wasn't the final solution, it was always temporary, they had already started building the steel water cooled plate before the first test flight. Based on the data they had available from the series of static fire tests leading up to the test they thought the concrete would ablate and survive one test flight before they took the downtime to replace it. Do you have any evidence to support your assertion that Elon overruled all the SpaceX engineers on the timing of when to install the steel water cooled plate or are you Literally making things up?
Learning more by moving quickly and taking calculated risks is clearly the better approach, as evidenced by the current dominance of the Falcon 9 and SN 25 and booster 9 sitting on a repaired OLM and being scheduled to make another orbital attempt in less than 2 weeks.