The only way to avoid that I know is to address a specific target audience and scale up to dominate that. Tumblr has achieved this. A rival then can't dislodge you because you already own the relevant network. It's still risky though, because if a rival builds a product that covers the general audience and also servers that subset well, then the subset might decamp. Hence Tumblr trying to break out of it's niche. G+ addressed a lot of niches very well, but Google just wasn't interested in that kind of network.
Shareholders care not for employee happiness, in so far as said employee is working and producing. Ditto with user happiness - if they're not happy they can leave. By not leaving, they must be happy to stay.
I think these proposals to "change" the metrics is as flawed as the current system.