R38 That's where I disagree with so many posters, who miss the point. May's apparent lack of intellectual sophistication hid a backbone of steel and the ability to outwit the ever so cultured and more sophisticated Countess Olenska.
May lies about when she absolutely knew she was pregnant to Ellen, knowing full well that Ellen would never push Newland into deserting not only his wife, but his child.
Those last scenes in the film, as Newland looks around the dinner table and realises that he is "a prisoner in the middle of an armed camp" and that "his wife is one of the plotters" who have engineered his separation from the Countess, and the scene afterward in the library when May tells Newland she is expecting (and admits to having told Ellen the same before the doctors confirmed it), exposes that May is perhaps shallow, but hardly stupid.
May is the winner in this contest of emotions. Newland, dismal as it seems, does the only thing he can do: honour his marital vows and his duties as a father.
I don't think the ending is at all pointless. It confirms that Newland couldn't quite break his ties with his background and culture to the extent that would have been necessary to join his life to Ellen's.
The last lines of narrative, as Newland realises that his wife understood what had been going on inside him, and appreciated the sacrifice he made on behalf of her and their children, and the knowledge removing iron bands from around his heart, make his last gesture toward the decision he made quite logical in terms of character.
"Tell her I'm old-fashioned. She'll understand."
And it's this sort of thing that made Wharton great as an author.
Henry James in Portrait of A Lady also explored the impact of character on choices of mates.
Thomas Hardy also explored it. So did Galsworthy. So did Tolstoy in Anna Karenina.
It's a very late 19th century theme.