Well, they first began with almost the same values. The difference is within default character/skill base calculation. Check level 80 weapons for this matter. When they made level 105 weapons, lot's of systems were introduced that have to be balanced somehow. I think that's the reason they differ so much.

But never make those values equal. You will notice the damage isn't the same.

The damage of a class (or race) doesn't come from weapons, but from the formula behind the character. It normally takes several inputs like status points (INT for shamans, obviously), and the influence of the weapon damage can be different from class to class as well.

From my perspective, more diversity for shaman weapons would be more interesting. Bells and fans are quite similar; they have different strengths, but the difference between ATK and MATK is always only some points. For better distinction between PvE and PvP, it would make sense to increase the gap. In other words, make bells more physical and fans more magical.

The damage from Shamans is not calculated the same way as other characters. Each character has some small particularities that affect the end result. The are mainly designed for PvM situations while the fans have better results in PvP because of higher Magic Attack. On top of that, from design, Shamans should not 100% have the same physical damage output as a Warrior or a Weaponry Sura.

agreed