That hasn't proven to be the case. People who were willing to use the black market before may go back, but in the states that have legalized the bulk of buyers are now people who never used the black market and would not chose to even with very high taxes.

Also lot of the most popular products are stuff the black market never really went into, like gummies, concentrates, etc.

That said, I think OR got it right at about 20% right now, though there's a bill proposed to raise that to ~30%, mostly to raise the local municipalities cut from 3% to 10%.