When Parker is targeted, he usually makes his quarterback look bad, and this goes back to Miami.
Here are his QB rating numbers when they pass to him, by season: 703, 98.5, 90.0, 86.3, 90.6, 60.8. (over the last 5+ years, because I cant' find stats from before that, but this includes his "good" years in Miami)
For his career, he has a success rate of 50.5%, a catch % of 58.6%. QB's have thrown 12 interceptions in the last 5+ years when targeting him (5 by Mac and 7 in Miami). This is over the course of 421 targets.
To put this in perspective.
Jakobi Meyers QB ratings by season: 91.4, 90.0, 81.0, 116.0 and 85.8.
He has a career success rate of 55.0%, a catch rate of 68.0%, his QB's have thrown 9 ints (2 by Cam, 3 by Mac over 2 years, and 4 this year in Vegas). This is over the course of 400 targets.