Most people care about their investment
Yes of course but this applies at any size. Someone who has worked his or her ass off to accumulate two dollars worth of SP may care about it more than a while with a million dollars worth. Don't be blinded (or attempt to blind) that "large" dollars figures somehow automatically convey some more sincere or "better" intent. They don't.
On Steem the incentives are counted in Steem. If people don't care about their Steem it's futile to try to predict their actions based on economics
Sure, and everyone can care or not care about their Steem. The amount being 'large' doesn't inherently change anything, except maybe how YOU perceive it.
So the majority shareholders have more to lose and should according to behavioral economics care about the net worth of the Steem network. Their own net worth health first pass by the value of the Steem rather than their reward.
That doesn't follow. It can apply (or not) equally to stakeholders of any size.
I've used the term more vested interest.
The amount matters. Different amounts will be perceived differently for people but what people value they don't want to lose.
Could you re-phrase that?
Someone with 2 STEEM may very well be as concerned, if not more concerned, about its value dropping than someone with 1 million STEEM. Pushing all of the influence over rewards to the latter an then relying on them having 'more to lose' from the value of STEEM decreasing is nonsense that does not work, both in theory and in practice.
There is no incentive of good stewardship that scales with the size of stake, as the whitepaper suggests (as do you). It's a false model.