I didn't have a bathtub floor on the AT and never got flooded out. I had to be careful about site selection.
Even when I have a shelter with bathtub floor I try to make it a rule to avoid setting up where my shelter might end up in standing water. I'm not going to bet that there aren't needle holes or pinholes in my floor that will let water in. I avoid packed ground, bare earth and low spots. I imagine what the area will look like if it pours.
That's just me.