Typically when we say WRs 3, 4, 5..... etc. we're talking about depth. DJ isn't depth. He's going to play the role of the deep threat WR like Brandin Cooks played. Only for about 20% of the money. That said, I don't see him getting a huge amount of snaps. It will likely be situational and according to the game plan to play against a particular D.
Rams are smart enough to know that you can't have him on the field too much.
