You are correct in your summation of potential damage, HOWEVER, as a BB potential damage is VERY important because that means you were a target that was tanking for your team, you weren't making cruisers and DD's be the ones that were getting shot at as you have a RP and many of them do not.
In other words, if I am in a BB all the way in the back and never get shot at, and all my cruisers and DDs die as a result, you didn't help your team as much as may think you have. Potential damage and damage output TOGETHER is a huge factor in which a ship or player can gage whether they did their job. If I have 3 million potential in a ship that players say "has horrible HP and armor" and I survived and dealt quite a bit of damage, then it is a VERY valid metric.
Furthermore, I played A LOT of battles in Oden in all iterations, I assure you, her HP being lowered was NOT as significant as everyone thinks.
-Hapa