I think one of the steps to move away from a GM culture would be to make mobs not have any immunities, save for cases in which it makes sense. Makes sense as in there should be an RP reason why a mob should be immune to certain skills/spells, rather than "because the mob is high level / a quest mob"
Of course, if this happens, there are some things that has to be set, eg.
-Mobs can only be stolen from once, period. If you succeed in stealing the Fabulous and Mighty Dragon Slaying Sword from the level 150 Balrog in the first try, then you can keep it. If not, you have to kill it.
-Directional spells should work on all mobs, BUT the mob should be able to track them. (Perhaps turn un-aggro if aggressive, and maybe return to its lair if not pursued by the player after a set amount of time.)
Because if you think about it, there are 8 different classes, and each class should have his (or her) unique way in vanquishing the obstacles in their path, possibly should be something like the below.
Priest - Heal spells, defensive spells, minor damage spells
Mage - Offensive status spells, offensive spells
Esper - Defensive status spells, Offensive status spells, Offensive spells
Thief - Steal, (if failure) Poison Weapon
Gypsy - Steal, (if failure), spells, tinkered weapons
Ranger - Not much unfortunately..Kick? Maybe upgrade bow/crossbow for it to be viable?
Hunter - Direct damage in combat, cure crit, behead
Warrior - Direct damage in combat, bash, cleave
Hmm, maybe meld pick lock and knock together into one skill/spell too. While 'pick lock' is the standard fare skill for rogue classes, it seems to have little importance here, because many doors are unpickable. Knock has the same restrictions as pick lock, but has the additional fact that it opens all openable doors, which is a rather convenient door opener for the lazy