Vesting has the unique property that before it occurs the shares are not yours and after it occurs, they clearly are (and can't be clawed back).
If you don't tax vesting, are you going to instead wait until the shares are sold to tax them? That would be very easy to abuse.
> If this provision becomes law, startup and growth tech companies will not be able to offer equity compensation to their employees.
Nothing stops you from offering it. It's up to the potential employee to accept it, weighing the possible tax liability.
> We will see equity compensation replaced with cash compensation and the ability to share in the wealth creation at your employer will be taken away.
In the vast majority of cases startup equity isn't worth the paper it's printed on. Paying their employee bonuses with cash would be a net win for their employees. The "losers" in this situation are established companies that arguably are already in a good position to pay out bonuses in cash (or at least include a cash component to cover taxes).
> This has profound implications for those who work in tech companies and equally profound implications for the competitiveness of the US tech sector.
I really doubt that. The talent pool, networks, and legal infrastructure in the USA are second to none. That's not going to suddenly shift because of minute changes to tax law.