This behavior of legal loopholes to discount workers should be made illegal. The definition of sub-contractor has got to change and/or have laws/policies in place that actually make sense in a sub contractor relationship. These are shell companies that spin up and exclusively deliver for amazon, they aren't gig workers delivering when they want, they have strict quotas.
edit: In the UK, we done worst of both worlds - exempted big corporations and "sub-contractors" can still be hired, but they don't have any employment rights.