@Zizel This is super wrong actually. You're comparing too much directly to each other, because NA 13* is the BIS. Nemesis and Slave are irrelevant even while being used to upgrade into Austere because Austere is worse than a lot of other 15* weapons nowadays -- AND ON TOP, JP just had a seasonal that dropped Nemesis and Slave like candy.
Look at the prices of Modules for Stil weaponry. That's a good example of how much you have to pay for top weapons. Hell, look at the price of various unit affixes like yamato factor and reveries (although due to new UH Emergency Quest, this has dropped a bit). Also look at Divine Order + Exceed Energy on a single weapon. I went back and sold a weapon that had that for 30m almost instantly. Hell, one of the most farmable affixes, Crack I, is one of the main ways I see people making money.
This is coming from someone who barely spent much on JP and so barely sold any fashion at all. And yet my units cost me around a billion to make, and then I've spent billions on fashion as well on JP.
Also Sky Dance Boon was literally 1.5 billion or something for the longest time on JP so yeah.