I would like to start by saying that I don't do PvP but I know some people who do therefore I may be significantly biased.
I like the idea of PMK items being exclusive to bigger kingdoms on Chaos. If all you need to do to introduce your own design is 150s and some unfinished items on hand then it's not fair towards kingdoms which have multiple players and deeds. Are Chaos players being greedy here? Perhaps. But I do think they deserve something from it. Running those kingdoms is not cheap and these items help a little bit with their budgets.
Moreover, if it was more difficult to make PMK gear it wouldn't make it any less inspirational to new players. I think it's on the contrary. The higher the necessary threshold to make these items is the more respect they inspire. I'm not against new content but I think that active kingdoms on Chaos should have something to ennoble them and the items of all these kingdoms lost in the past should have some history "attached" to them a well. I still remember that when I was more newbish than I am now my good friend, Clasin, showed me some old wagons of kigdoms defeated long time ago and told stories about them. It was fascinating to look at the unique designs and listen about things and moments lost forever in time.
Now imagine the world where anyone can make a design for a wagon and make dozens or hundreds of copies as long as he pays enough money. The market would be overrun with different designs and the only trait distinguishing individual designs would be the art. Nobody would care to keep track of designs specific to Chaos kingdoms. Perhaps people wouldn't even bring many wagons from Chaos to PvE because nobody would want to buy them. I suppose there would be more competition for better designs but that would only make things worse for the Chaos kingdoms if they wanted to sell their own gear.
So in the end it's highly subjective but I believe that PMKs do deserve an oligopoly on some player made designs.