Sensitivity is almost always measured at 1000 hz -- therefore it is largely irrelevant to sub bass. Typically, in my testing, a higher sensitivity driver has a gain only above 50 hz or so in a given box volume. This is not SUB bass... below 50 Hz is where a sub-woofer should be doing it's thing outside of an SPL competition.
Absolutely not true -- see my testing. Hoffman's Iron Law... from small box, high sensitivity, and good low-end you can pick two of them. In car audio you want a small box and good low-end therefore cannot have a high sensitivity. This is a law of audio design -- not a theory -- and I've verified it in measurements.
I suggest reading the thread I linked to see the data for yourself.
A very strong motor and/or a lower mass can both do it -- both of which reduce low-end extension. Typically why you see PA drivers with such high sensitivity -- both a light mass AND powerful motor.
In home audio enclosure volume is not critical like car audio -- see Hoffman's Iron Law again. They pick sensitivity and low-end so box size is sacrificed.