Yeah, those videos are awesome, a total beatdown of a supposedly hard MVP boss. iRO wiki says that Celine Kimi has 444 MDEF originally, so without MDEF piercing this cuts 73.5% from magic attacks, so almost 3/4 of the damages are gone. Even if half of the MDEF is bypassed, with 222 MDEF she still receives about 62% reduction in damage. This is a direct result of the flawed MDEF scaling in renewal, and hence why 100% MDEF piercing is needed, or at least close to 100%(90% or more).
She's actually not that bad with 78% bypass (card combo + +9 obmh).
No comparison to 100% but still totally easy and doable.