I don't think things are that bad actually...
The arcane ring has 4 fundamental qualities that makes it so disired and highly priced:

#1 Extremely rare: not only because it is defined as "arcane" but also because there are very very very few of them ingame.
#2 The best item: Yes the arcane ring is currently the best item compaired to any other right now. Nothing can beat it.
#3 Hard to create: The quest to create it is one of the most tedious and time taking.
#4 New: It just came out. Anything that is new and few initially is highly priced even if it a pair of green useless daggers.

Adding this to the fact Parth arcane ring was "perfectly perfect" with the rarest gems ingame it is only obvious it would cost a huge amount of gold.
As for the other arcane and mythic items they are currently accessible only through merching and farming w/o the help of plats so let us not genaralize a case and apply it to all the others.