For Myrrh, I actually don't mind it! Except that her Boon is HP. If it was -ATK/+DEF, I would be a very happy camper.
Overall, -ATK as a bane has very nice uses depending on char and boon. For my glass cannon -Blade mages, I STRICTLY prefer -ATK/+SPD. The only time I dread -ATK is on low ATK chars like Merric...