Your WRs should be fine. U may be able to improve them to a small degree but that aint your issue. 

Like u said, you likely have players open at times but you dont see them. U need to find a few setups you like that stress the user on D. Go lab the small handful of plays against diff coverages u til you have read progressions down.

If you get that down, you can keep doing it or slowly add new arrows to your quiver