User blog comment:Gourgeist/Shingeki no Kyojin Chapter 66 Review: Wish/@comment-3203692-20150212184159/@comment-7418318-20150223222656

I wonder if Lod really believes that Eren can never unlock the full powers of his Titan form.

WIth him not inheriting the memories and personality of the ancestral line, maybe he just has to learn the stuff by himself first instead of instantly gaining the knowledge through the memories. If that's the case, it's as you said a better solution, since he can use those powers at his own judgement without being influenced/controlled/possessed by another person.

With the past custodians of that power you could never know if it really was their decision to not fight or if they were unable to follow their own will.