From my experience, if an app takes more than a few months to build and launch, the risk is no longer worth it. Large companies also do this (years building before launching and i have yet to hear of a success)
You wider point is reasonable though as many people waste a lot of time building something that never gets traction.
I think it's also important to recognize how much survivorship bias there is in these stories, too, though.
There are plenty of people who have spent similar amounts of time working on games or projects with nothing much to show for it. The experience might be worth something to someone, though, in terms of resume building, etc.
By contrast, most apps need to connect to people, software and things outside themselves - they're part of complex systems, and it's really hard to know if they work well without putting them into use and seeing how they perform - and that means selling and talking to users, not something you can do in isolation.
In 2020, realizing it was going nowhere, I started talking more with my target audience. Really talking and really listening. It turned out that most of them had a very specific pain point.
I thought about how to solve it. I could build another gigantic app. Or I could start as small as possible. I could write a tiny script that addressed that pain point, and do everything else by hand.
If I knew it would scale to x, I might have started with more. But I realized I'm bad at predicting what will take off, so I started as small as I could.
This year I'm getting close to $1K MRR. It's not much in the grand scheme of things, but coming from no business experience, it means a lot to me.
My biggest takeaway so far is, for those like me who don't have an incredibly clear vision, start as small as possible. Not "if you build it, they will come," but "when they come, you can build it."