It wouldn't surprise me if the change to one narrow fairway on #9 coincided with the installation of an irrigation system. As for the steepness of the ground... It's not too steep, other than near the rock out crop that separates the two fairways, far away from the cliff's edge. Depending on one's errant drive, there are times when playing to the very end of that old fairway is the prudent play because the angle is so good and the distance to the green manageable.
There's actually two swale/riparian's on 9. One is farther back towards the bottom of the hill, where there were bunkers on the left side. Maybe at the 130 yard mark?
#10 actually came to mind when I played Pac Dunes #4 for the first time. (save for the straight coast line) The cut outs of hillsides that Pebble's 10th has all along the right are excellent features, especially the one about 50 yards short of the green.
From the old 10th teeing ground, directly behind the ninth green, the hole was sublime. Moving the teeing ground up the hill has lost the heroic nature of the tee ball caused by those scalloped cut outs up coast. They are are just as intimidating as the swale on #9. So in comparison, the tee shot on 9 is not as hard as the tenth tee shot, but the approach to #9 is much more testing than the approach to #10.
These two hole's ebbs and flows are so perfect, and as such, are a big reason why I respectfully disagree with Paul Cowley's suggested changes.