As far as I have previously seen in the forums, that is not the correct interpretation of the special skill percentage. That percentage also goes inside ‘Att’ calculations. This is easy to prove from your video. If you see the first time Jackal attacked the titan he did a damage of 701 with Wilbur activated.
So that is given by: 100×(2.7×765×1.15÷(1000×0.56))^1.35 = 703 (close enough)
If what you are saying is correct, his damage should have been:
2.7×100×(765×1.15÷560)^1.35 = 496 (which is not correct)
As for the rest, when there are two defense debuffs, the elemental one is chosen if the colour matches the debuff. That is why Eve+Lianna or Jackal+Joon are such effective combos.
Also, note that Tarlak and Miki attack buffs don’t apply to special skills, they only apply to normal attacks (that is tile damage).