What do you mean by "fake" and "custom"? Nearly no gear is "custom" in the sense that it's custom made for a specific person (although some small manufacturers probably would do that, if you're willing to pay for it), and at least in electronic music gear it is not a common claim for it to be (and it's e.g. not mentioned in the article here, so I'm not sure why you are arguing against it being so?)
Similarly, what's "fake"? The product is what it says on the tin, is it not? I think you overestimate the "can be build cheaply" aspect for many small manufacturers too, given small volumes, need to pay for R&D, mechanical components/work, ...
What does fake usually mean? Deceptive maybe? I think a lot of what is being sold isn't substantial. It isn't supported by utility, but other things like marketing.
I think a lot of the market for these items aren't people who need it. Being e.g. modular is something of utility. These products usually requires assembly because those who made it didn't have that capability, they share parts with something else or they are customizable from the start. Not because the manufacturer decided that it was a good idea for marketing purposes.
What does custom usually mean? I guess that is a bit harder. You could probably say non generic. It is something that was made for some specific purpose or could be adapted to specific situations. Maybe they don't say it is custom, but that is most of the point with a modular synth. That you have many specific modules that could be changed. Either by making a better one or in how you combine them.
My argument is partly about the product itself. That it is using features of custom things without really being it. You get to assemble it, but not because it lets you customize anything or because it is really needed. You get modules that you can use in other product, but the product itself isn't really modular.
The other part is about the market in general. There is a paradox in luxury goods in that they can't have to much utility. Because things with utility doesn't usually have a lot, or as much, margin. This type of gear can only be expensive if it doesn't have that much utility. Otherwise someone would make it far cheaper. The utility of the product is to some extent being expensive.
And note that I am yet again not saying that there is something wrong with this as such. Not that this help since it still offends. It is just that when you are pretending that something is something that it isn't you are hurting the real thing. I think the same is true in other areas as well, as open source. Or being a hacker.
If anyone can say that they are doing these things no one has to really care about the real thing. As I said earlier Stockholm is awful for scrappy companies. Yet, people can point at a company like teenage engineering and say "look they are doing these dynamic things with utility, how bad could it be?". But in reality there garage work space was in the most expensive part of town and apparently filled with one of the founder sports cars.
So if there is anything I would want you to take away from this it is to not give up the real thing. A dynamic ecosystem were people can actually modify their tools and make new things. This is were all these movements get their reputation from. Being a catalyst of other things. Not by having people play pretend with expensive things with less utility.
Like the top comment implied, if you want to make music learn a DAW. You want to make your own synth as a hobby, do that (there are a number of great forums). If you want to have a company in Stockholm, where apartment costs as much as in SV, sell you expensive gear go with this instead.
Similarly, what's "fake"? The product is what it says on the tin, is it not? I think you overestimate the "can be build cheaply" aspect for many small manufacturers too, given small volumes, need to pay for R&D, mechanical components/work, ...