I understand what you're saying. What I'm saying is that his height and wingspan complicate that statistic. He doesn't have hands of golden stickum, but he's not a "dropsies" guy, either. It's just that he can reach passes that guys without his size could not, which would be considered inaccurate passes for the purposes of the calculation.
Say a QB throws a 100 passes each to Parker and a smaller receiver. 20 of them are off target, outside the smaller WRs catch radius. Same 20 passes, 10 of them are inside Parkers. Say Parker can't pull in any of those 20. Both Parker and the smaller WR catch 60 of the 80 "good" balls. The smaller WR would have a catch % of 60/80 (75%) while Parker would have 60/90 (66%). But are you actually worse off with Parker? No, you've lost nothing.
He's far from perfect, but is he a significant upgrade in our top 3 WRs? Very likely.
I love Bourne, so cheers on that.