To me, the didn't need necessarily more time to develop Dany but better writing. In the final episode she is talking crazy, from that big speech, to alone with Jon, when she says she knows what good is because she knows what good is. She didn't need to be violent, but they needed to show that she was losing grip on reality, and what kind of world she actually desired; that could have been feathered in throughout the season, without any additional episodes.