Minimalism is about maintaining useful purpose behind the things you own and not retaining unnecessary objects. If you're a DIY person, and you have a good reason for a backyard of junk cars, that's explainable. If you buy a new iPhone every year but you don't actually use the majority of the new features (if ever at all), that's frivolity.
Minimalism isn't the ideology that (less is more)==(less things). That comes from people appropriating philosophies to compete for attention on social media, where everything is at best one-dimensional because the point is to entertain not educate. No, minimalism as a philosophy means (less is more)==(object-essentialism). You initialize solutions among what you have, and factor the time, resource, and opportunity cost into the cost-benefit of acquiring a new object. So, as I mentioned, if acquiring a backyard of junk cars is more cost-benefit savvy than having to acquire a new junk car every time you need a resource from one, it's minimalist. However, if you acquire a junk car that adds what you already have a sufficient amount of, it's frivolity.
So minimalism is just efficiency? Call it that then.
And frivolity isn't a relevant category to minimalism. You could be minimalist in achieving frivolous ends. Clearly you're carrying too much in the term.
It is hard to avoid no true Scotsman territory for a term that in not very well defined and used slightly differently depending on context (what medium, which aspect of life, geographically). Also I haven't read any of the linked books/articles the newrepublic piece links.
Wikipedia has it as: "The term minimalist often colloquially refers to anything that is spare or stripped to its essentials."
Oxford Dictionary as: "a style of art, music or design that uses very simple ideas or a very small number of simple elements"
So in my opinion, having rusting car wrecks around in an old shed with the intent to re-use their essential spare parts later is perfectly compatible with minimalism, and what I would expect someone with the skill set and space to do so.
Contrast that with a large garage where numerous expensive cars are being parked and continuously maintained as well as cost of electricity, cleaning, security etc. for the building, although the cars are pretty much never driven.
That would be much closer to a minimalists nightmare. Not the self reliant utilitarian guy with the old shed.
The comparison is between having a single working car that you pay someone to fix when it breaks vs. owning a car that you can fix by yourself by having lots of tools and parts around.
The first is minimalist because it involves less physical material to store and organize. The second is self reliant because you can do for yourself without needing to draw on outside systems as much.
The example you gave is just moving the goal posts completely. The large many car garage case is both less minimalist and less self reliant, so not to the point.
Not at all.