well obviously it can't be 100% jade for a couple of reasons.
1. Nel has a minimum of 2 or 3 bars by the time you reach the dark world
2. Glace can have 2 permanent bars at some point during her quest line.
You are correct that escaping any of the 3 dark world spirits is quite difficult due to being unable to struggle during combat.
A relavent note is the timeout on struggling is a real time lockout from being unable to attempt again so if you skip through the lewd action in non combat scenes you will likely end up back in combat before you can struggle again i think.