I assume you mean because swerve is a bigger factor in those shots and swerve is harder to estimate.
Both of those things are true, but remember that the amount of swerve is the same with either kind of shaft, so its effect on any shot should be equally difficult to estimate.
Also, because swerve is a challenge we tend to shoot at speeds that minimize it, making squirt a bigger part of the aiming problem and squirt reduction more effective.
pj
chgo
And.. the CB seems easy to spin out line?? Me anyway..