My perception is different.

It was appropriate, I think, for the FAA not to ground the fleet after the first crash. It was also arguably appropriate for the FAA not to ground the fleet immediately after the second crash, but then after some time when it became apparent that the failure mode was sufficiently similar (as they did).

However, what has emerged since then certainly damaged the reputation of the FAA. But it was not a matter of a few hours, it was a matter of careful investigation and evaluation over months.