I think you could read the rule of pride to say that apprentices are fully exempt, so that while a graduated runesmith can't even duplicate an item with a single rune, an apprentice can make any duplicates they want.
The 'easy' answer would then be to declare that standards have slipped since Thungni's day, and that almost every living Runesmith is still only an apprentice by traditional standards (Bok may give some evidence for that view), and in their own pride and hubris have mistakenly been thinking the Rune of Pride applies to them when they're not worthy of it.
Under this model, you'd pick up the perpetual apprentice model from the Colleges (and possibly the runepokers' relaxed recruitment standards) and most members of Guild of Runesmiths would spend all or most of their time as apprentices. Only the most talented researchers would be 'promoted' and so be subject to the Rune of Pride.
Pretty sure demotion wouldn't fly and would be a lot more radical than what even Thorek is proposing. His swarm of apprentices model would work even with the restrictive rules on duplication (except for the one where every runed item has to be unique - which very much reads like an game abstraction that's logically contradicted by immediately stating that apprentices can copy runes).
The problem comes with other Master Runesmiths not having apprentice swarms* - which would be excusable if they'd all be a third as good as Kragg but they aren't.
*As a theory as to how this state of things came to be: to deal with massive losses in the time of Woes the Guild might have promoted lots of less skilled Runesmiths who then focused on mastering Battle Runes. Then when the dust was somewhat settled the survivors realised they lost a lot of knowledge - particularly knowledge less relevant for combat and that they weren't capable of recreating that so they trained their apprentices narrowly for warmaking and then those apprentices lost more lore and became even pickier with their apprentices, as the relative importance of runesmithing declined, until nowadays most of the Guild is comprised of has-beens of has-beens.
As a side note, I'll have to look it up, but I think I've seen mention that Thorek isn't the only Runelord in Karak Azul. He may be the most prominent, but he has peers there. I wonder if they're on the same page as him. I dimly reflect this in the context of Anvils of Power, saying that not only do multiple Runelords have them in Azul, but so do some particularly elderly and skilled regular Runesmiths, but they just use them for crafting and don't take them onto the battlefield.
They'd likely be his apprentices or juniors so not exactly peers.