It is difficult to survive a direct hit from an EF4 or EF5 even with a warning. When you have these storms rolling through densely populated areas like they did today, there's nowhere to go. There are very few basements in the southeast due to the water table. You get in an interior room and try to protect yourself from a roof collapse but your wood-frame building is going to get blown to smithereens. The only warning good enough to avoid this is one that comes early enough for evacuation.
Personally, if I had been in the path in Birmingham and seen what happened in Tuscaloosa, I would have checked the traffic cams for congestion and gotten out of town. There's no way I'm going to try riding out an EF-4 or EF-5 in a wood-frame house if I had 40 minutes to evacuate. There are a lot more things that could be done with regard to these monster long-track tornadoes to avoid loss of life. I think the advice to stay in your bathtub and wait for an EF-5 to hit you is just insane. I use the bathroom for smaller events and quick spin-ups but that is not usually the case in these massive events.