I think it's a bit of both, but moreso the former as opposed to the latter...
I've seen this year after year...the ball distribution is more realistic when CTH is set at 50, simply because that slider affects ALL aspects of receiver play...
Route Running / AWR / etc.
It also gives the CPU QB more "perceived confidence" in their ability to "make a play"...as well as just having more total "points" in the total passing subcategory (the total of QBA / PBK / CTH), so all THREE things take a minor bump in the process...
At lower values, the AI is going to go for the "safer" option more often, for the reasons above...the secondary option becomes the primary option, passes into the flats to TE's as opposed to the higher rated guys...
With having OPI at 100 against DPI at 98, I could get more balls to the WRs, but this is much more effective...
That being said: having it "balanced" against the PCV puts the receivers on "equal footing" with the players covering them...
It's not totally unlike that balance we shoot for using the DPI / OPI settings...
All THAT being said:
I could kick myself for waiting until baseball season to figure out what should have be set at default from the jump...
Oh well!
Lastly: it's pretty easy to "test" the difference...
All anyone has to do is plug in a slider set (that they are very familiar with) that has both HUM and CPU CTH at 45 and then change both those values to 50...
BOOM
EDIT of EDIT:
Didn't work as hoped and all attempts to adjust things in a way that included this setting set the set into "reverse"...