The good thing about the dive bomb sight is you can use it to practice your level bombing calibration. Since it is continuously computed, if you are in the bomb sight, you can look through and see exactly where you bombs would land. If you calibrate your bombsight, then flip out of calibration mode, the two should match up, if you did a proper calibration. If not, the difference is the error in your calibration.
Using the dive-bomb point like this is very useful since you can calibrate over and over and over just to get some practice and not actually have to release a single bomb.
You are right, using the jabo sight too much can make you rely on it for dive-bombing, but at least it gives you some ideas of where to aim. It's like training wheels though, once you get the hang of dive-bombing you should drop using the sight.
-Soda
The Assassins.