I think the fact that you are moving the suspension very close to the droop bumpstops and therefore hitting them all the time is the primary reason for the perceived stiffer/firmer/rougher ride.

Yes, the angles of the A-arms play a role, but I don't think they play as significant a role as you seem to think or imply. IOW, the difference between the "X" and "Y" lengths in your picture don't change significantly enough to matter or be noticable. Say our A-arms are 12" long ("X") and are horizontal at stock ride height. Now add 2" of lift from cranking or spacers. Your "Y" length is now 11.83", which is only a 1.5% change in length. 3" would be 11.62" or 3.2%. Not significant, IMO.

But yes, I do agree that adding spacers or cranking the bars does not increase or change the spring rate.