I don't know if I'd call him selfish (and if he is, he's no more selfish than most other players). But I suspect there is both a selfish and a selfless side, and he's torn between the two. Part of him wants to do anything possible to help his team win. The other part wants to do anything possible to maximize his value as a free agent. And in this day and age, that means above all else hit as many homeruns as you can. He's trying a bit too hard to hit homeruns, particularly with two strikes. That's the selfish side. But as I said it doesn't make him any different that many other players.
I think you're reading way too much into it.
I've talked about this before my ban on ES, but Harper is his own best friend and his own worst enemy. He lives inside his own head. So when things are going great, he's amazing. 2015 is a great example. Locked in and focused at the plate. The first half of last season was like that.
But when he scuffles, he simply can't get out of the funk like a lot of guys do. And they are truly bad funks. Then he starts to try and overcompensate by hitting big home runs.
Add to that a rather complicated swing, and he seems like the type that will always struggle with consistency.