This has been a truth in the game since I started playing right before VF was launched live. Players who had played 4 or more years who were generally my guildies/teachers said that it had been true for a long time, particularly once you passed about Colonial Age. They also spoke of how hard it was to acquire any lower era goods when AF came out as it was introduced in 3 stages over a fairly long period of time. I would imagine that a huge goods' crunch also occured when OF was introduced simply due to the massive tech tree. (Of course, this was before neighborhood streamlining and it wasn't at all strange or unusual to have EMA players in the same neighborhoods with AF players and everything in between).
I think as SAM was introduced and then the next eras, it seemed like the days of the Big Goods' Traders either flooding or crippling the market began to wane. It might have also had to do with so many crack-downs on Push Accounts + the advent of the then brand new feature: Guild Battlegrounds. Not every having advanced any of my cities past AF and that's only 1 of 4 fairly active/developed cities for their eras, I'm not sure that I could speak to it on a personal level for the higher era goods since I rarely, if ever, deal with them but I do know that there was a massive change in the ability to obtain very low era goods ever since the Arc Frenzy started about 2-1/3 to 3-years ago when practically every IA city dropped an Arc in it's tiny little yard and then people started power-leveling them to 80 before they even got to COL. Nowadays, it seems hard to find anyone who actually stays in the lower eras more than a few weeks or maybe months at a time. So in TE/FE in my two more active cities (FE city being my primary), I find it almost impossible to acquire any goods below about PE or sometimes FE unless I happen to have friends in the lower eras.
The last two weeks of GE5 have just made what was already difficult even harder. I suspect y'all may be right that the after-effects of such drastic changes in the game one right after the other in the last couple of months will not bode well on the goods market. (GE5, premium bldgs in events only available thru $ purchase, and the mobile ad-blasts that have caused so many people to quit the game entirely).
Not sure at all where this is all going to lead but I know from my one world that I'm in a big guild on: The expense of GE5 isn't really stopping anyone from doing most/all of the encounters. It's like some kind of fever! The market is reflecting it as much as seeing problems in our treasury (and friends say the same thing from my other worlds) - why? Because all of those goods they'd normally donate to the treasury are being dumped into negos on GE5, I'd suspect. IDK - too soon to tell but I sure don't have a good feeling about it.