User blog comment:Omega natsu2/Chapter 369: The Place Prayers Reach, Predictions./@comment-31.132.65.50-20140129025714/@comment-24467372-20140129173925

Well,speaking in MP terms yes. His Magical Power was weakened. Other than that,he was fine and he managed to hold out against an enraged Erza perfectly fine.

Waayyy more than %1,right? If Siegrain was just half of his MP or even 2/3 of it......how powerful was this guy?

We're basically agreeing but we have different terminology concepts in mind. I'd call his state after using Self Destruct magic on himself a "weakened state" rather than the absence of his MP during ToH