In my opinion it is wrong to unlock the NPC only after an Orkham clear. It's an element of the game that should be accessible to every player. Every player can enter the Arcane Forge, but about 60-70% of the server cannot use these stones, they sacrifice time, charges and gold to sell them to the other 30%.
They are of the same value, but they are sold at different prices, Corrupted Tiers are always cheaper than normal ones, which is because only certain players can use them.