What's the real conclusion of Cather's O Pioneers!?

It seems that Willa Cather backs off from the darkness visible that she builds toward through the first 4 sections of O Pioneers!, her 1917 novel that begins as a celebration of the stark beauty of the Nebraska prairie and of the pioneer spirit that drove the first settlers to struggle and succeed - but over time the novel evolves as we see the fractures the split apart the Bergson family, the jealousy and the sexism, the misery of those who yearn to get away, the narrow-mindedness of those who stay on the prairie, building finally to a great eruption of violence as a poorly educated, crude farmer kills his wife and the man who'd fallen in love w/ her - not the ending we would have anticipated from the first glowing chapters. Yet it's not the end of the novel; in the final section, called Alexandra after the central character in the novel, the woman who successfully runs the wheat farm but in the process sacrifices any possibility she may have had for a family life of her own, goes to visit Frank, the farmer who killed her brother in a fit of jealousy, now in prison in the state capital. Perhaps oddly, Alexandra says she understands what he did, that her brother was wrong, and that she will devote her life to seeking a pardon for Frank. These are noble sentiments, perhaps, but it brings the novel to an even darker place; Alexandra leaves Lincoln for her small town shuddering in horror - she was repulsed by the visit to the prison, and she seems to have no direction - and then she gets a telegram from Carl, whom she has had a crush on since childhood, who's gone off to the Alaskan gold fields. Carl (?) read of the sensational murders in a West Coast newspaper and immediately headed back for his home town, presumably to console Alexandra. The novel ends w/ the two of them kissing (lightly) on the lips and looking out across the wheat fields. So, yes, it's a romantic conclusion, they will probably marry and continue managing the farm, or at least Alexandra will. Carl speaks about returning to Alaska together - he'd entrusted his share of the business to his presumably reliable partner. But do we believe any of this? Hardly - it's obvious that he's an incompetent, that she will continue to do all the work, that he will gradually become resentful, that there's no great sexual chemistry between the two of them, that he will stray or wander or even leave for Alaska, once again, alone. Cather sees this, too, one would think - of all writers she is completely aware that a powerful woman like Alexandra would not be a match for a weakling like Carl, or perhaps for any man. The true conclusion of the novel, had Cather the courage to write it at this point early in her career, would be Alexandra alone.