In a very general sense, our QB plays to the level of his receivers. There really weren't any weak links in the receiving corps in 2016, and Dak had his best season.
In 2017, Dez was not the player he was in 2016, and this happened.
2017
to Bryant
52% 829 yd 6 td 5 int 71.6
to everyone else
66% 2468 yd 16 td 8 int 91.3
In 2018, the team went into the season without an outside WR who had played with the team previously (except for TWill, who ended up with a total of 3 targets), and this happened in the first 7 games.
2018 (games 1-7)
to Hurns/Gallup/Thompson/Austin
52% 563 yds 3 td 3 int 74.2*
to everyone else
67% 837 yds 4 td 1 int 91.7
Enter Amari Cooper, and this happened...
2018 (since game 7)
to Cooper
70% 725 yd 6 td 2 int 115.2
to everyone else
70% 2064 yd 10 td 3 int 97.2
I said "very general sense" because there were obviously other factors that affected Prescott's performance (OL personnel, outside help with his mechanics) but you can basically say he has played to the level of his receivers. That's encouraging, especially if Gallup continues to develop.
*This doesn't count the shovel pass to Austin for a TD, which was only technically a pass attempt. If you count that as a pass, the rating goes up to 79.