Yes, but what counts as a defect?
Humans are far from the only creatures that can reason. We are just better at it than most other creatures.
IIRC Aquinas' view of the soul was not as simple as you make it sound - even the 'vegetative soul', though dependent on the body, isn't part of the body but attached to it. He had a well-organised model of biological life, but it is just wrong. The difference between life and death is a matter of biology, cellular metabolism, biochemistry. The 'sensitive soul' and 'rational soul' are interesting concepts as metaphors, but not useful as practical real-world descriptions.