"The tax system is designed by permanent salaried employees on PAYE at HMRC based on the nature of work as they know it"
Which is exactly the point of the statement "Build a modern tax system" - Government controls HMRC (OK, don't laugh) so government can engage (employ, outsource, or whatever) knowledgeable people in the real world to create a tax system that reflects the true nature of work and remuneration. The current system is >100 years old without major overhall and is no longer fit for purpose.
Note, I don't include PWC, EY, Capita, or any of the other self-interested Consultancy majors as suitable for the job.