A union would provide the sort of employment protections much of Europe alreadys enjoys.

I know how Unions work. The OP stated: ...it's time for you to toss that leadership out. You can do that by leaving, or talking to management about this, or unionizing.

A Union can organize and sustain a strike. But they cannot "toss leadership out". Not the CEO, the Board or any manager at any level.

They could theorethically "blackmail" a company saying "strike will not end until X is fired" where X is a PM or manager or whatever but I never really heard of anyone trying this tactic, not to say actually succeed...

Unfortunately union / labor movements in the US suffer from a big problem: due to historical circumstances they’re very combative. The labor movement here never grafted the idea of being business oriented on behalf of workers into the movement (like in Germany) rather, they treat the business as the enemy pretty much from the outset.

Some of that is indeed earned by the businesses reputation, but ultimately this is what I think spurred the decline of union membership in the US because businesses don’t get a lot if any value out of having a union around and the organized workers often find the benefits stagnant after some time

That is because of historical circumstances, but it continues to this day because it's encoded in the law; we don't have codetermination or sectoral bargaining.

Police unions are very business oriented. And they might be the most successful unions