Rosario can get away with it because he provides some really nice defensive value, and some speed as well. Arcia provides no defensive value, his only value is through his bat, which means if you are going to be a corner OF with no defensive value, your OPS+ each year needs to be in the 115-125 range IMO,if it's any lower, the team should be looking for an upgrade. Which is why I think he needs to continue to improve in order to be a long term asset for the Twins and not just a 1-2 season stop gap, the only way to improve is by getting reps every day.