There is not some guaranteed power dynamic.
Business is not all huge companies with infinite redundancy. There are 30M small businesses in America that employ 60M people. For the vast majority of businesses and teams, losing an employee hurts, and employees have lots of leverage. These business owners have to do the work to ensure redundancy, to plan their budgets and products and systems to ensure they can weather inevitable employee turnover. Plenty of businesses fail to do this and have to close their doors. It happens with regularity.
On the flip side, unemployment is the US is super low. It's true that workers can only hold one job at a time, but they are not "trapped" at a job. In fact, they have more mobility than ever, which also gives them leverage to negotiate for higher salaries or to hop jobs. Not to mention more gig jobs, remote jobs, and contract jobs than ever, even for highly paid positions. Sure, losing a job hurts. But the employees who plan for this possibility, who maintain skills, maintain savings, and live within their means, can find new jobs, just as businesses who plan well can weather employee turnover.
It goes both ways.
So if you're in a position where your employer has some huge power dynamic hold on you, is that some universal truth for all employees resulting from the nature of the employer-employee dynamic? I don't think so. I think that's the result of poor personal decisions, or bad luck at best.
All that said, I'm 100% on board with legal protections that set a high standard for employers. We have plenty of those already. And I'm 100% on board with government stepping in to help take care of people who fall through the cracks. For example, I love that COBRA allowed me to stay on my previous employer-provided group healthcare plan for 18 months(!) after my last job ended.
What I'm against is any cultural or legal change that begins to suggest that its employers' responsibility to keep their people employed. It's not. Financially, the system can't work that way. Employers are not our parents or our nannies or our caretakers, and we should not try to make them into that.