User blog comment:Rjwstar/MGQ world`s various untold informations - Torotoro blog Q&A/@comment-26228098-20160115214727/@comment-25707465-20160117083415

26. Is actually not really a plot hole if you consider holy energy has a certain influence on its surrounding, particularly on living beings (Heinrich body being destroyed because he was bathed into holy energy is the basis for this hypothesis). So it's possible that if Alice punched Ilias while being "contaminated" by the weapon's aura lead to said wound.

It can also means that monster can't use Angel Halo for long since its inherent "holy corrosive" attribute would be particularly nasty for them. Don't know if TrTr thought that one out completely though.