I’m equally sure that wherever the line is placed in law, companies will often elect to run right up to, but not over, the line. This will often be worse for employees than just getting it over with.

I sincerely disagree. Even just slowing down the churn rate would give more employees a chance to find other jobs without a "can't make rent" gun pointed at their heads. It would also avoid flooding the market of this or that sector, which exacerbates all problems around joblessness.

Policy doesn't need to be perfect, it just needs to push in directions different from naked market forces.