At its core,

[wufwugy]

Do they work? As evidenced by what?
What specific morals from what specific stories have worked?
What do you mean by asserting they "work?"

They survived. My hypothesis is that the archetypes and the morals that are widely distributed and prevalent in old literature that developed over millions of years exemplify ideals that humankind evolved for. Here's an example of the type of thing I mean:

Why does the knight kill the dragon to save the virgin? Probably because our ancestors' survival came in part by adapting to a dominance hierarchy in which the bravest and strongest males -- who killed or figured out how to kill predators -- were sexually selected for by and reproduced with females. It can be extracted from this that discarding the morals of this story and others like it probably leads down a path of poor survivability and poor happiness (due to misalignment with natural being). If there is any moral that is objective amongst humans, it might be the kind we evolved for, the kind that aided our survival. How do we discover what those morals are? Old stories is one way.

It should be noted that lots of old stories are probably poorly interpreted. For example, the traditional Christian view of the Garden of Eden is eating the fruit is a loss of innocence and a transgressing against literal father-God-creator. If we use Jordan Peterson's interpretation, which in my estimation is far more astute, the view of the story is along the lines of to see the snake in your own heart you have to open your eyes. The Bible and lots of other myths track this idea roughly, such that it appears the deepest moral for human survivability is some sort of amalgamation of the logos, of honesty, of sacrificing oneself for the greater good/truth.

Seems like if the classics had it all sewn up, there would have been no side-track to anything else.

They for sure do not have it all sewn up. Using what we can from archetypes and morals that are millions of years in the making is a good start.

There's good stuff to interpret from old stories. There's a connection to people who lived eons before you facing similar difficult choices, finding love, failing at it, and finding new love.. etc.

There's also ridiculously bad stuff in old stories. The Bible is full of rape stories, the old Greek tragedies are full of rape stories, etc.

I agree broadly that there are common threads to humanity, but I don't agree that simply because something is old, it has intrinsic value, or that the value it claimed to have when it was originated is still the value it has today.

I agree. My words are regarding caution towards discarding them so easily. I'm not saying you're doing that. I don't think you are. I do think contemporary western culture has sunk its head in the postmodern ground and stuffed ears full of sand by discarding old stories at large. The popular idea that humans are progressing to greater morality away from the caveman morality of the past is just not sophisticated enough for me.