I don't think its true that all startups are for all founders. We realized that the "right" track for this startup was "build software, get a large sales team to distribute it". That particular profile of a business didn't suit us.
In some regards your criticism is right: Founders get into a startup without necessarily knowing what paths lead to success. The most probable path to success was one we didn't feel we were good for. You might say that a really tenacious founder ought chase any thread that leads to success -- and that our unwillingness to do so is a founder deficiency.
I happen to be interested in lower variance, possibly lower EV opportunities. I don't want to roll the dice for 2 years for a chance at a big exit.
"Startup" means a lot of different things, so I think its pretty hard to identify someone as ill-suited for "startups in general". There are a thousand ways to skin a cat; pick the one that works for you and keep doing it.
The OP mentioned 'founder-startup' fit, but I wonder what kind of startup trajectory they were expecting. Nothing is formulaic about a startup, but it sounded like they had close to the standard success case as possible. They launched a product, they got some customers, they got information from those customers, they realized future growth would require a pivot in their product but that growth could easily dwarf what they had done before, and... well, that sounded like a lot of work and they punted.
The Spaciety team launched a product, got customers, got revenue, and had a seemingly clear path to more growth via investment and product enhancements/pivots, so despite shutting down I would actually consider them a success. But I finished reading this and was mostly left wondering what trajectory the OP and his founders were looking for? Very few startups had a story like, "well we put in a lot of time to launch the product, got some customers, so now we just kind of hang out and let it run itself and we probably have a 50% chance to sell for like $3 million."
The OP talks about founder-startup fit, but were they a bad fit for Spaciety or a bad fit for starting a startup in general?