I don’t think there ever was a rule which said mages couldn’t wear armor in warcraft, that sounds more like DnD lore bleeding into a headcannon.
considering we have spellbreakers who are magic wielding warrors, and had dalaran battle mages since WotLK who wear armor which is classed as cloth but looks armored.
The problem for me is that right now, Blizzard seems unwilling to take a firm stand in either direction, leaving us with only awkward compromises.
We can’t transmog across armour types, but we’re given a plethora of cosmetic options that allow us to look like we’re doing so. Similarly, we’re holding onto the faction divide, but it’s being steadily hollowed out to the point where it no longer makes any sense that it exists.
I’d much rather prefer Blizzard pick one or the other and go hard. Either enforce armour types or let them go. Strengthen the factions or dissolve them.
This is also funny because Blizzard in the past said no to freeing any restrictions because they didn’t want people making clown mogs. However, they’ve now put out (for real money sometimes!) things like murloc and yeti onesies, so they’ve also been contradicting themselves in this regard.
I don’t think this is necessarily the same as the faction divide (and likely it exists due to game systems? Perhaps that’s the issue for transmog too, who knows how intrinsic armour types and factions are to the code).
This wasn’t making sense since Vanilla. We had race-specific archetypes that were essentially multiclasses even back in the strategy, but sadly, one didn’t have a chance even to mimic an NPC’s appearance until recently. Say, how would you treat a Blademaster? A mage for the mirror images or a warrior for the iconic 2handers? Or the moon priestess, should she be a druid, a hunter or a priest? And the same goes on and on…
It’s RPG lore.
https://warcraft.wiki.gg/wiki/Warmage#In_the_RPG
Oh, fair enough 
Which itself borrows from D&D’s gameplay balancing armour system (if they just allowed mages in the TTRPG to use plate then you’d have very-high AC casters immediately). It doesn’t surprise me that people cling to it, mind you, its very much a staple that “casters wear cloth”, for understandable reasons but the argument has always been a wonky one in WoW itself since. . .
Well, Paladin in Vanilla was considered more of a cloth-wearer than a plate-wearer, despite being advertised and treated like a plate-wearing class by the Devs back then and today, Shaman often had a similar issue horde-side.
Where the actual lore is concerned, we have a description of Battlemages ca. Second War as follows:
His armor was a battered as any, but consisted of a breastplate bolted over a crimson set of scholar’s robes, of the type that would not have been out of place in the halls of the Kirin Tor. The hem, sleeves, and vest of these crimson robes were inscribed with runes of power—some of which Khadgar recognized, but others which seemed alien to him. The leader’s snowy beard reached almost to his waist, obscuring the armor beneath, and he wore a red skullcap with a single golden gem on the brow. He held a gem-tipped staff in one hand, and a dark red sword in the other.
It was a normal sight for mages to wear a breastplate over their robes to protect their vital organs, but they remained primarily spellcasters first and foremost and not some weird spellblade hybrid that people often try to pass them as.
It is indeed part of the WoW RPG copypasting 3,5 D&D rules.
Easy solution.
Let mages dual-wield so we get to be Gandalf instead of D&D mages.
I can’t speak for shamans because, well, that’s kind of their vibe. Fur and robes. But paladins in vanilla were not considered more of a cloth-wearer beyond people choosing to wear cloth pieces because it helped with their spec, with only the Judgement set standing out amongst a sea of very clearly plate armour.
Just put 5 levels into eldritch knight (7 if you want war magic), rest into wizard.
There are/were a number of offhand stave items back in vanilla, which could be ‘dualwielded’ with swords for the gandalf vibe.
Of course you can’t hit people with the stick, but it’s a walking stick. He said so himself.
What’s worse is that WoW doesn’t even let mages be D&D mages.
D&D mages, as commonly depicted in art, wave their staves or wands around when casting. Warcraft mages have their weapons glued to their backs, while their casting animations have spells shooting out out of their bare hands.
FFXIV got it right (arcanist animations are my personal favorite with them holding the book aloft). It’s one of the reasons the in-game mage class just didn’t gel with me, as much as I like mages in lore.
WoWs animations, although better (in some cases) than they were, still irk me.
I think part of it is because they nearly all have to be useable while moving. It makes so many of them lack any form of weight. Like you’re using a nerfbat weapon. And yeah, magic users never using their staves etc is annoying as heck.
The staff on a mage’s back is an arcane antenna to amplify the ambient energies. Or something. Damn, just let me wave my stupid stat stick around…
The technology is here and has been since at least Legion, bundling staff wiggling with signature artefact abilities. Just bake that into a select few spells and fix that idle combat animation.
Speaking of, is there any news on a fix for the duplicated legion weapon mogs?
Yup, it was mostly done due to all of the stats that no longer exist in the game.
Same applied for stuff like warriors in wrath double dipping between plate and leather pieces, if I remember correctly they and rogues were having full on fights about a pair of armor pen bracers from ICC.
Also strength being feral druid’s 2nd best stat back then too.
Expertise and Hit Rating too my behated.
Hilariously: still is in SoD. But yeah, Paladins would normally wear pieces of cloth for intellect, spellpower and mana-regen since it was the only way as barely any Plate in the game had it. Shamans would often wear leather for maximum-agility alongside mail, Feral Druids were fighting with WARRIORS over strength gear because it was better than agility gear etc.
Remember that with paladins, yeah.
Also remember being a mix of mail and leather on my shaman.
Classic weirdly had a lot more freedom of armour and a lot more flavour in general despite being the oldest version of the game.