I think you're underestimating the value of an OPS around .800 in the current offensive environment. From a quick glance at BB Ref, it looks like Santander was 6th in OPS in all of baseball among players whose primary position was RF (a couple of spots lower if you include guys who spent time in RF, but it wasn't their primary position). I think Cowser and HK both have the potential to exceed that, but it's certainly not a given that one or both actually does so, especially this year.