AFAIK, Deviling was not available through OCA ever on heRO. It was on iRO before the removal of the miniboss-ring cards. However eAthena had a bug where it was only Ghostring and Angeling and I think heRO jumped from an old SVN (with that bug) right to the removal during an SVN update.
- Bio3 used to be much easier but still the same experience. Mobs were solo-able by non-trans characters fairly easily. This was like 8 years ago, Bio3 has long since been more fun / harder.