I'm an INTP 5w4.
The issue that you're seeing is related to the cognitive functions being inaccurate. A lot of people interested in personality types have learned that someone's functions must be ordered in a symmetrical way of alternating introversion and extroversion, such as Fi, Ne, Si, Te. According to this idea, if someone's dominate function is a thinking one, their fourth function must be a feeling one; furthermore, if someone's secondary function is a sensing one, their tertiary function must be an intuitive one, and so on. Despite the fact that these ideas of the cognitive functions are present all throughout personality forums, they are actually a myth.
The biggest issue with the cognitive functions is that it contradicts with everything that is known about psychology and biology to assume that someone's personality would be so perfectly symmetrical. In actuality, biology and psychology are usually a lot messier and chaotic than the cognitive functions would lead you to think. For example, it's biologically possible that someone's four main cognitive functions might look something like: Te, Ni, Fe, Ti. There is no evidence that someone's cognitive functions must be laid out in the way that most people believe, and basing things on what is known about biology, it's more likely that someone's personality would be a lot less organized than this.
All we can really do in comparing someone's MBTI and their Enneagram type is compare the Enneagram type with the traits dictated by the four letters of the MBTI. In doing this, I think it's definitely uncommon for any 5w4s to be extroverted types, as introversion and seclusion tends to be a trait of 5s. It also seems to be relatively uncommon for sensing types to be 5s, as sensors that think a lot tend to do so in more practical ways. Overall, I think that INxx types are more likely to be type fives than anyone else.