The big X that you speak of may already be on the roster in Justin Shorter.
6'4 235 and runs a 4.45.
True Bills fans have already forgotten about him because he had a hard time getting on the field with Gabe and Sherfield ahead of him. There was just too much depth last season.
That won't be the case this season as Shorter will have a good chance of getting playing time.
Also you could move Shakir to the big X position and have Shorter back up both him and Diggs.
Then go grab McConkey at 28, play him at slot and have Harty back him up.
The big X that folks are looking for won't be on the board at the end of the first round or later.
So go grab a really good slot that knows how to get open and can help Josh out