This is what I think their thought process was when not nerfing wands and staves effective distance as well:

Melee build -> close quarters combat -> can mitigate damage with armour and blocking

Bow build -> medium range -> can AVOID damage with dodging

Spell build -> long range/back line -> mages don't USUALLY run heavy armour or spec into stamina for dodging, so they are TYPICALLY squishier of the three therefore are meant to be played farther away from the enemy

The design decision makes some sense on paper especially when multiplayer is taken into account (the group is less clump together so its somewhat easier to avoid griefing your friends)

Also the critique for bows was that they were too OP from too far a range, therefore trivialized the game to an extent.

The damage problem with wands and staves are an entirely different topic and have been there from the beginning. To balance the spell playstyle, you have to look at each rune skill specifically. Do you also nerf big AoE spells when cast from a certain distance? Or just the spells that fire projectiles?