You're overlooking something quite crucial about Jake's "heroism". It wasn't his body on the line, it was his avatar's. If that qualifies as heroism then I want the Congressional Medal of Honor for all the stunts I pull in Halo.
And if he loses his avatar, he just gets to enjoy being a paraplegic. That really is overlooking something crucial. All criticisms of Avatar for weak or cliche story have failed miserably. Like this one, they all involve ignoring huge parts of the movie or just plain making stuff up.
Speaking of making stuff up, Jake does not get to keep his avatar by playing both sides. He gets to keep his avatar by, first, Trudy airlifting the portable lab, and second, the intercession of Eywa. Otherwise, choosing to help the Na'vi would have lost him his avatar. Given that means going back to being a full time paraplegic, his choice is motivated by more than vanity and self love. Trying to turn his choice into vanity and self love is a perversion of logic. It is either stupid or dishonest, not an enviable position to be in.
Jake doesn't begin as so selfless a person, of course. But the insistence that Jake start as noble and finish, what, even nobler? That really would be inferior storytelling. The implications of Avatar for the contemporary world can always be evaded by just saying its just scifi, or the old standby, just a movie. But those implications are part of the movie. Jake's journey is part of the audience's journey to a new perspective, which makes him a suitable viewpoint character. Jake is not a compelling character like Quarritch or Neytiri because he has to also be Everyman, albeit an Everyman who becomes heroic, to be the audience viewpoint character. Not liking the destination and refusing to go along does not change that at all. You could criticize the movie for offering us cheap self vindication as heroic people like Jake, Trudy, Grace and company. That is
not the criticism being made and never has been. Draw the conclusion, folks.
And, as ever, ignoring the the fact that Jake doesn't succeed in saving himself, much less the Na'vi, minimizes the overall plotline leading to Na'vi victory. The Na'vi victory is a huge emotional high point in the film. Neytiri has to be someone Jake (and we) could love, and be a personal stake in the action, but she has nothing to do with the victory. Part of the objection to Jake is that he isn't the Mighty Whitey who wins the day. Given the Na'vi path to victory is a major part of the movie, Jake isn't quite as central as claimed, but Grace is not just someone to ignore.
Last and least, narcissism in everyday language does imply pathological, just as I said. Implying I defined narcissism is itself an example of a strawman. And dragging in the APA is pretty hyperbolic.