Trump doesn't like to lose. If he thought he would lose, he wouldn't be in the game. If it were ego, and he just plain and simple wasn't concerned about the $$$, he would have run long ago. Let's face it: Other than Cruz, the field this year is extremely weak - the same old ho hum GOPe CoC candidates running - nothing of them at all exciting. And America is tired of the same old same old from Repubicrats. He gains NOTHING to run just for his ego, and stands to lose that AND $$$ if he loses.
Oh, I have no doubt he’s in it to win, at this point....
But I think pride/ego/competitiveness are the *main* motivator, not the only one.
I think your points - and mine- are all valid, except that he might not have all that much to lose, he can make more money pretty easily from what I’ve seen.