Being a good negotiator isn’t going to overturn a shareholder vote or a board decision. You’re trying to say that corporate governance doesn’t exist because in some cases it can be inefficient.

In practice, management can get minority shareholders to approve almost anything, the most obvious being by treating unreturned proxy ballots as implicit votes for management. They can entertain floor resolutions (never put before shareholders on proxy ballots) at investor meetings in locales they choose, but which they know will be burdensome or foolish for shareholders to attend, because they plane ticket alone would wipe out any expected earnings on their shares over the next 100 years.

And that's just in the nominially shareholder-democratic sphere of things that are actually brought before shareholders. Most things simply aren't, and furthermore, in public companies, management essentially CAN'T tell shareholders more than is required by the SEC, because that means making the information public, for their competitors to see and plan around.

In short, shareholder democracy "sounds good, doesn't work." Management has total, dictatorial power, except in the case of major institutional investors like mutual fund managers or investment banks, who often as a matter of policy always support management. Even when they don't, they're so far removed from the people whose money it is that they're using to exercise their power that they may as well be classed with the manager class. Rarely, very wealthy individuals can exercise substations control as investors. More often, they are management as well (e.g. Zuckerberg's control of Facebook is as a manager, not as a shareholder.)

Clearly, a single employee or customer of a large company might not be in a good negotiating position, but an organized group of workers or customers might be able to influence the governance of a company. Organization might come about in a formal way, e.g., a labor union, or informally through the spread of ideas.