> A worker must be permanently hired after the first extension.

After the first extension the worker will not be hired again.

> Agencies can not be used indefinitely

Yes they can.

> A company is also not allowed to make an employee 'self-employed' by making them start their own company.

Wrong. I've seen this happening personally.

> I'm just talking about holland here but all over europe the conditions are similar.

You're talking about what you think is happening in Netherlands, and the conditions in many places in the rest of Europe are not like that.

> But those are mostly for in-between gig jobs. Not for stuff people make a career out of.

Not yet.