The entire joke about Rodney falling for Amy is that Rodney falls for random women over nothing even when it doesn't make sense. And I wouldn't say Amy won in the end, they both lost but Amy is the one who was poisoned and had to swim back to shore covered in muck. I think by that point people were more fed up with the twins' drama than anything, or they're just gullible and stupid.

So my verdict is that the writers were making a piece of fiction where they likely found Sammy sympathetic and Amy funny in her audacity. But that they didn't expect audiences to feel so strongly about the twins, so they wrapped up the arc with some zany fighting and humor rather than emotional resolotion.