I think it's easier to make a fullback out of a winger than a half. Wingers know they need pace, they know they have to run in support to provide options, particularly second phase play. They also have to learn positioning in defence, such as when to drop back for kicks.
Moltzen simply does not seem to have the basics down. Coming into the line to create overlaps in attack, acting as a second five eighth, these things are bonuses compared to positioning yourself correctly to take bombs, scoop up grubbers, defuse other kicks and then running the ball back hard.
Nothing that I've seen from Moltzen in the past indicates he can do these things and we need a fullback who can do these things. If we're not going to use our juniors like Meaney, we should look at importing a player who can do these things, someone who is on the fringe or the outer at other clubs, some like Kevin Locke, Isaac Gordon or even Wes Naiqama who is playing out of his skin at the Knights.