There is a legal requirement for directors of public companies to act in the financial interests of all shareholders. In practice, and according to precedent, this means long term viability of the company, in other words, a sustained profitable business.
There is no such requirement for a private company. In practice (esp. recent history), this means private equity firms acquire successful businesses to "mine them" of their wealth - capitalizing their assets for personal gain, and leaving nothing left.
The question for public companies isn't how many retail vs institutional investors they have, it's whether an investor can make a claim about a breach of fiduciary duty. It's patently false to say that the institutional investors (who yes, do have more sway) aren't interested in the company acting in their financial interests.