That illustrates the basic limitation with something like PFF where they are just looking at play on tape without knowing either the player's responsibilities or why the player has been given a certain job.
Consider the PFF viewpoint. If Flowers gives a 15 yard cushion to Hopkins and then comes up and makes a good tackle after a 10 yard completion, that is him executing the assignment given to him by the coaching staff perfectly. PFF probably gave him a ++ for all of those.
Of course, the reason why he was giving a 15 yard cushion was because if he had given anything less, then Hopkins would have run past him for a touchdown and he would have scored a -- on that play. So the coaching staff playing him deep means that they get the blame from sites like PFF instead of Flowers.
Hopefully, most fans realize that the real problem is our backup CB needing to cover DeAndre Hopkins. Better depth at key positions is why we dominated the 49ers yesterday, and it's very encouraging going forwards.