I trust my own eye as much as anyone else's in most instances - you have to remember, that for the guys making these calls, batting .500 is a pretty good average. A lot of these players will bust - and GM's and scouts will be fired. It's how the business works.
That said, it doesn't take a scout see that a guy isn't physical, or that his misses tackles - if a team, i.e. the GM and scouts think the guy's positives outweigh his negatives, and think they can correct the negatives, they may give the guy a higher grade. A lot of it is preference of style and scheme.
The Packers historically like DB's with better balls skills, and physicality and tackling don't matter as much; hence, it makes sense that they would give a guy like Randall a higher grade than most. The Packers are a finesse team - I happen to hate that style of play, especially on defense, but it is what it is.
I'm much higher on Rollins, who is the antithesis of Randall. While Randall would rather stand back and watch others make the tackle, Rollins is a tough and sure tackler - so taking both of them back to back is a bit of head scratcher.
I think Randall has a very tough transition in front of him. He played facing the LOS, his back pedal is questionable, his hips are questionable, and his make up speed is questionable. He probably would be better at Safety, but then his poor tackling and lack of physicality would show up more. I think he's going to struggle more than Rollins, even though Rollins is much more inexperienced.