I believe 1B is an easier position to play. Call me whatever names you want, but that is my belief. There are only three non-pitchers in the last 20 years that I can remember being close to as tall as Duran- Richie Sexson, Adam Dunn, and Corey Hart. Two of them were clearly 1B and the other one (Hart- who is quite fast) is reportedly going to see more and more time at 1B beginning this season. Players that tall are usually not all that mobile (Hart is the exception) and height is a big advantage at 1B (bigger target).
Mark my words, Duran's future (if he has one) will be at 1B. Maybe not this year or next, but eventually.
Think of mobility as the least common denominator of defensive skill. You have to be able to move to get from A to B to fetch the ball. But that does not mean that the less mobility the position requires, the easier the position. If that were the case, catcher would be easiest and CF would be hardest.
The fact that Duran may flunk OF does not mean he would not also flunk 1B. He will, if given the chance, IMO. There is little question in my mind that 1B is not his eventual position -- it's DH.