I want to preface this comment with the following: Sal Frelick is my favorite player on the team. I truly believe he sacrifices his body on defense. He is short in stature and I have a soft spot in my heart for the little guys. Also when he was coming up, many fans were calling for him to be called up because he was doing so well in the minors. He is also a great guy.
Unfortunately, he has not lived up to expectations. Is that because he is limited due to his stature? Is it because too many people have been in his ear this year about, I dunno, hitting more homers? I'm not sure. His swing has certainly changed this year. I don't recall him swinging an going to a knee as much he has this year. That swing shows how much he is (almost literally) swinging out of his shoes.
All I know is the numbers don't lie.
My thought is that when Lockridge comes back, Perkins gets sent down. Lockridge will be groomed to be the next right fielder, and Frelick will be moved to a bench role.
Be careful when saying, "Bring up the next great guy from the minors." As Sal (and others) have proven, minor league success doesn't always translate to major league success.