Melodies are insufficient on their own in my opinion, the court rules differently I guess. Melodies are just as likely to be formulaic, and are built using similar foundational knowledge as a chord progression (only a subset of notes works in a given progression for example, and conventions lead you toward certain notes of that subset).

A combination of chords, melody, rhythm are I think the only reasonable measure that a song has been copied.

Lyrics and melody? I think that's reasonable to consider that an infringement. Melody over a new chord progression? I do think that should be considered a new work, just to limit the scope of copyright. Even if it's clear you copied the melody, I think melody alone is insufficient to call a song. Unless the original song was entirely melody. A melody is using all the same musical building blocks as the chord progressions did, why does it get special treatment?