It's hard to imagine Prometheus without Rapace. Her performance was acclaimed and with good reason. She had an inner strength and physical ability far beyond what Portman has. Portman is a fine actress, but she is more vulnerable and less physical. On the other hand, if Portman had played the part, Covenant would never have existed. Instead, we would have had Prometheus 2, it would have come out years earlier, had a bigger budget, and would have been massively better than Covenant, imo. But I'm still glad Rapace played Shaw. She was the right choice for the role.