The Dutch tax service keeps trying to figure out new rules of how to distinguish between true self-employed people and fake self-employeds who basically function as regular employees, but without the rights and benefits of employees. This is mainly meant to protect excessive exploitation of low-paid (gig-economy) workers, but it certainly limits my options as well.

I'm self-employed and tend to work for a single client at a time, usually on projects of between half a year and two years. I work on a team with employees, doing similar work, except I'm more empowered, more in control of my own way of working (also because the tax service demands that, which is good in this case). I'm not being exploited the way employees or gig workers are. And if the government thinks this is some kind of tax loophole, I'd happily pay more tax, as long as I can continue working this way.

For a startup you probably don't have the capital / financial support to ensure redundancy packages etc.

If you need someone to come in on your greenfield project and hit the ground running, thats what contractors are usually used for; the beginning and the end of the lifecycle.

No, they're still solid jobs compared to what lots of other people get paid. But managers and other corporate types still get paid a lot more. And self-employed, you can also get paid that much, just not as an employee.