Heath Miller does not have the athleticism or separation ability to get off the line quickly and get into position for a fade or flag route inside the 20. Miller is good player over the middle because he is a mis-match for LB’s, but he is not quick enough or athletic enough to be on the outside and out jump a CB for a TD.
Also, you can’t throw a pass blind over the middle to Miller if you are in trouble because there are too many bad things that can happen. Using a tall WR out on the boundary, you can blindly throw it to the corner of the end zone and you have the sideline and endline to protect you from INT, that is not the case in the middle of the field.
Also, the funny thing about this is Plex (and most tall WR’s) play a completely different position than a smallish player who is not blazing fast like Hines. Plex is a Split End, plays outside, stretches the field, uses mis-matches to make long plays. Hines is a flanker (sometimes referred to as a slot) that plays inside, off the line of scrimmage (so he doesn’t get jammed) and works the middle of the field as more of a possession style receiver.
Basically, this is like Ben saying “Damn, we could really use a big bruising fullback” and then Willie Parker getting upset about it. They both play what is called “running back” but they are drastically different positions.