I'm only addressing this from a legal standpoint.
In a court of law, jurors are not allowed to do their own investigations. They are expected to rely entirely on expert witnesses for any sort of expertise.
The standard doesn't say they would have to be able to tell it was a copy without someone pointing the elements were copied.
Sherlock Holmes declared his method "Elementary"
, and it was, no matter how obscure the clues - once you know what to look for.
I believe a competent "musical expert" could convince a jury that they could tell that a piece of music was copied from a song... mostly because it actually was
copied, so the elements are there to be found.
Would an average listener come to that conclusion on their own? I seriously doubt it.
And I'm certainly not arguing that any of this is beneficial to the making of music. It seems to me that many of the recent rulings are likely to have a chilling effect on music making.
I'm just suggesting that the "legal perspective" can be much
different than what we might consider a more "common sense" approach would look like.