>He could unilaterally decide that quarterly profits, hell, any profits, do not matter and there is nothing anyone could do.

That’s not entirely accurate, see Henry Ford suspending shareholder dividends, raising employee wages and lowering price of cars for consumers to fulfill vision of every American family owning a (Ford) car.

Shareholders sued and won because Ford owed and violated his duty to shareholders.

Since that time the Law has evolved to extend director/officer protections - even allowing officers to raid corporate funds to ensure directors re-elect the officers - but The voting rights don’t relieve Zuck of his duties to other shareholders in his capacity as director and/or officer.