Maybe Holdo was the first person to think up the kamakizee lightspeed attack. As others have pointed out kamakizee is only useful in certain situations, it makes sense no one would have thought of it until now. They did say she was a brilliant general, and Poe + Hux (both experienced in the military) are confused when she turns the ship around.
Heck, Anakin in a The Clone Wars episode crashes a Republic Cruiser into a Sepratist blockade, almost sacrificing himself.