I don't totally agree, but I would have preferred a slower death of the character.
I would have liked her to face Emma in the final battle but, however, we don't have to forget that it's all about the message in OUAT. She actually face the Black Fairy when she was in the asylum but she faced her powers unconsciously. Snow, David and the others faced her powers head on and we really saw the extent of her power and her dangerousness in the EF ! We must not forget that she destroyed entire worlds during a period and thus killed millions and millions of people, all in order to gain infinite power. Thanks to her, we have one of the biggest major stake of the whole series : the destruction of the magical worlds with frightening apocalyptic plans and a scenario as amazing and surprising as the one we saw in Avengers Infinity War. It was epic, totally new, unexpected and grandiose for a final OUAT battle. Thanks to the Black Fairy.
Moreover, the fact that Emma faces Gideon shows that only the light can destroy the light, so facing the Black Fairy directly wouldn't have made sense and the fact that it was Rumple who kills her makes a nice echo to the death of her father that he kills too in my opinion.
But I totally agree with the fact that I would have liked to see a little more of her powers in action.