User blog comment:SoulRise99/Chapter 526: August is the REAL child of Zeref and Mavis; as well as the WEAKEST Mage in Alvarez!?/@comment-125.212.122.68-20170313232229

His inability to replicate holder magic only means that he has to use the other caster magic spells that he has copied, not that holder magic suddenly deals special damage to him. To be fair though, there remains the question as to whether he is tough enough to survive a holder magic attack (and it would really be underwhelming if his 'special' magic power has the drawback of being too sensitive, thus making him really fragile)