I'm speaking from personal experience, having significant knowledge of the FAMICOM homebrew market, particularly in Japan, as well as in the American and European regions.
Having developed several NES + FAMICOM games myself, I've consistently observed that the NES versions consistently outsell their Japanese counterparts.
While it's true that some countries utilize FAMICOM carts through FAMIclone systems, in my opinion, attempting to sell games in these regions isn't practical due to the complexities of production costs versus sale prices. While it's possible to manufacture a small quantity of 20-30 copies at low cost, this doesn't constitute what I would consider a viable market opportunity.
On the other hand, in the USA and Europe, there's a robust market for NES games, with hundreds being sold, pricy complete in-box versions.
This is really off topic, but here is just a bit more food for thought.
It is logical that the NES versions will outsell the Famicom versions, as the majority of the western-developed homebrew is being marketed towards American and (Western) European regions. I suspect that there are several different reasons for this, including differing tastes in games, language barrier, etc especially when dealing with the Japanese market. Similarly most American and European collectors are going to choose a 72 pin version over a Famicom version, something that has even been seen with many prefering "reproductions" of Famicom-exclusive games to the original versions.
The Famicom homebrew situation is emerging / growing, the NES homebrew scene is booming. A few years ago we didn't even have molds for Famicom cartridge shells, but that problem had been overcome for NES homebrew probably over a decade ago. Similarly, many (western) authors don't offer their games on Famicom format - oddly enough though, Mind Kids and a bunch of other shady companies on Aliexpress have been offering Famiclone releases, suggesting that there is some kind of demand. For the record though, I don't agree with stealing and then bootlegging the efforts of homebrew / indie developers.
I guess what I am saying is as someone who has been following Famicom / Famiclone homebrew history since its infancy, I definitely see that is has come a long way since 2014, which was around the time I had first started advocating for Famicom homebrew releases. I also developed and released several Famicom games - the people in Taiwan, Thailand, Argentina, etc are generally shocked as they haven't really been introduced to homebrew culture yet, though it has started to hit places like Russia and Poland a bit. So I would say we are an emerging market, whereas America and western Europe are established markets.
Anyways, I'm a fan of the games you and your son did, and although I don't necessary agree with your opinions here, it's really hard to say how things will ultimately be in ten or even five years.