[yummyfajitas]

The management within a company (considered as a class, rather than as a singular entity "the company") does indeed bargain collectively with the workers of that company.

If that's what he meant, I have no dispute. But, like you say, I can't see how that matters.

And it's pretty clear who has more leverage in the labor market: corporations. Replacing a worker is annoying but the corporation can usually afford to do without for a few months, whereas losing your job for even a short while can be devastating.

I don't think this is clear. Losing your job for a while can be devastating if you haven't planned for it, but the same is true of an unprepared company losing a valuable employee. Some empirics are necessary.

Also, it's only an effective monopsony if workers are incapable of searching for other work while they are employed.