im not talking about the oven holding an even temp, most of them are pretty good at doing that
im talking about having even temps in different spots of the oven, especially if you're holding it in a rack over a roasting pan. you'll almost never get even browning in an oven, and air is a terrible conductor of energy, so it takes longer to brown anything in an oven regardless, while the meat continues to cook internally.
wrapping it in paper would just steam the meat and give you no browning whatsoever.