Not everyone on the Mets is playing at their natural positions. Daniel Murphy is a natural third baseman who can also play first base. However, he is now a second baseman because of the presence of both David Wright at third base and Davis at first base.
Duda is a natural first baseman himself. However, he has been playing in the outfield for the past few years thanks to Davis being a first baseman. Why didn't Davis have to learn a new position? It's because he was already a much better defensive first baseman.
In his rookie season, Davis wowed Mets fans everywhere with three separate catches over the dugout rail at Citi Field. His defensive skills took immediate notice, and he is definitely capable of winning at least three or four Gold Glove Awards during his career. In fact, he is likely the favorite to win the award this year.
Davis' fielding percentage in the major leagues has never been lower than .993 in a single season. He has 1,045 putouts in 1,114 chances with 61 assists as well. Davis has always played very well in bunt situations, throws well for a first baseman and is great with making diving catches as well.
Duda, on the other hand, is not as skilled defensively at first base. He is larger and less agile than Davis, which means that he cannot cover as much ground. This would explain why he has had trouble doing so in the outfield.
Furthermore, Davis throws left-handed, while Duda does not. As a result, Davis has yet another advantage because of pickoff throws being easier for left-handed throwers to swipe on base-runners.
The Mets over the years have had overweight first basemen that have made countless errors and have simply not done well in the field. Former Met Mo Vaughn would certainly come to mind. Duda may not be as big as Vaughn was, but again, there was a reason why he was converted into an outfielder instead of Davis.