This is really pretty simple. There's what Adam has said and what he's actually done. He appeared to be the nice guy in Average Joe I, but he was chasing after a woman who was much more similar to Samantha than Rachel.
What did Adam actually have in common with Melana and what was it he liked about her? Mostly America saw reasons to like Adam and the fact that guys were supposed to find Melana attractive.
I don't know that Samantha has much in common with Melana other than a kind of "need to be rescued and protected quality"....I think of Adam helping Melana get over her fear of being on the glider (which was one of the first times anyone rooted for Adam) and Adam bailing out Samantha the day trader (I think he likely steered her away from buying stock in the company Adam Sandler worked for in the movie Anger Management and talked her into buy stock in cosmetic surgery and tanning equipment companies) as very smilar episodes.
Adam falls for the lady because he rescues or protects her in some ways.
Rachel did exactly the opposite. She took control, cooks breakfast, writes the poem, takes care of his mom during her crying spree.
Adam's beein in a protective family his entire life. His picture of a family/mate for him is someone he can protect or rescue as his mother and father did for him.
Rachel=Adam's sister in his head.