We're still paying taxes, the only difference is that the client isn't paying for it, and maybe there is a bit of a discount for starters.
As a fractional/freelancer, I enjoy the freedom and mutual expectation that I'm in this for the money and for the short term. (In my case it gives me the resources to bootstrap my own product company).
In NL the regulations for false self-employment (enforcement kicks in January 1st) is primarily aimed at low-wage jobs like meal delivery etc. High paid professionals with multiple clients per week (like most fractionals are) are not the target.