That's not true. A pyramid scheme, legally, has no product but itself. Those are illegal.
For example, pay me $20 to join my company and you get the right to recruit people for $20!
Amway is essentially exactly the same except they add a product to the mix to get around the law. They still primarily profit from the "employees" rather than customers.
Changing the definition of a pyramid scheme, for the proposes of law enforcement, to something more akin to "profits primarily off employees" is what needs to be done.
If you have model legislation handy, particularly the specific legal definition of scams like MLM, I'd be very grateful. Otherwise I'll poke around a bit, to see how UK phrased it.