well, not elemental, but Jumbo Flan required magic to beat. though it might not have been immune to Aeon overdrives i cant remember.

is it not better if super bosses absorb elemental attacks?

i would like a tournment in an FF game in which u can get drawn against many diff super bosses. and it would be cool if the hardest super boss can summon lesser super bosses at will to help, and allow the super boss some limit break counter *materia* of sum kind. that way it will counter limit breaks with 20 ultimas . oh and max defense, all status causing attacks and millions of hp has become as standard now.