"Legitimate interest" is a very specific term in context of GDPR. Not a lawyer, but have been looking into it previously, and I doubt "we want to feed data to our AI so we can make more money" passes the Legitimate Interest Assesment (LIA) test.
Here's an example of a test that must pass (sorry, docx, but way better than a random explainer): https://ico.org.uk/media2/for-organisations/forms/2258435/gd...