Empress Morgana chose Rex for his brutal and domineering fighting style.
His fiery temperament in battle—along with his innate ability to regenerate could scare the monsters of the void. Not to mention, despite not being immune to pain, Rex didn't hesitate in getting bloody, taking on attacks with unnerving closeness.
From the eyes of the voidal monsters, he was extremely menacing.
After all, the voidal monsters banked on their innate advantage provided by the Black Rift to regenerate from any injuries. Be it a mere cut to something grievous like losing a limb, the voidal prowess allowed them to regenerate, some even needing seconds.
Generally, spirits didn't have that kind of advantage.
All of them fought carefully, relying on their Soul Artifact more instead of clashing outright.
