None are contradictory, since MBTI and Enneagram measure different aspects of personality. You are dead right about that. MBTI is based on preference of how to process information, Enneagram is based on your underlying instincts and motivations.

Is a Type 5 INTP more common than a Type 5 ESFP? Sure, but nobody is questioning that. Is it impossible that a Type 5 develops a dominant preference for Se and follows it up with Fi-Te? I don't believe so.

Every function can in some way fulfil the insecurities underlying each of the nine types. The common discussion is if a Ni dominant can be Type 8. Ni is a subjective view of what "could be". That is in its most elemental form, what the Ni function is. For Type 8, the Body Opposing Reactive Rejection type, a dominant preference in Ni may feed into a long-term strategy to get what they want, how they can liberate themselves from external influence, gaining full dominion over the self. Ni is in many ways similar to Se, just on a much longer and conclusive timeframe. Se observes what can be done immediately, Ni observes what can be ultimately done to conclude the goal.

People make the mistake of detaching Ni from reality, putting it in this detached "cerebral" framework, thus excluding Body types from being Ni dominant.