The mystic was Ronan and as for the rest of the team I don't recall but I do know there were no aura's affecting her. And she was not in the back ranks at the time of the attack. I would really like to see the math on a mystic with a 10,000 defense, with my rough calculations at most your looking at around 8,000 and that's assuming her faith was Krotos, all the runes she had were defense and every single piece of gear she had was defense. And if that's the case how did she do 7,500 points of damage with her sanctuary of runes skill? Th a skill is at 120% of her mag stat. If everything she had was defense and defense only there is no way that could have happened. This why I'd really like to see the stats because it appears it simply does not add up.
If that is RM Ronan, he can hit I think 12k DEF at most Max LBed with Athena faith and max insignia of the nymph. There is also the damage reduction talent for mystics which is a decent 30%.
If you are in lower-middle tiers, that player might be a whale who isn't climbing the ladders. I had some experience of maxxed opponents before when I was fairly new occasionally.