Meh, I dunno... apart from the hyper-religious context... those 4 Agreements seem like a fairly sound basis for quality living.
I am intrigued about your comment about psychology and mythology. My favorite author/thinker in psychology, James Hillman, reminds us of a very salient fact - the mythology of the ancient world was their psychology, the psychology of our modern era is our mythology.

Don Miguel Ruiz is a Toltec Master (Mayan) not sure where you are getting this. The four agreements are an extremely helpful tool. I worked for two of his students and ran an entire treatment program based on them. I assure you God did not come into the teaching.

Forget the Four Agreements and all the other mumbo jumbo adjust don't be an asshole you will be a happier more mentally stable person.

Yes. See 'How to Win Friends and Influence People' 1936.

NPR had some speaker talking about how what we classify as mentally ill in our society as a birthing of a Spiritual Shaman needing guidance from an experienced Shaman.

If something is true it really doesn't matter who says it. The same for falsehoods. Religion can be devious in claiming credit where it's not due and I guess it's up to us to point out when they do so. That's our job.

The Dalai Lama has said:

"World peace must first come through inner peace." (And yet there's little investment in mental health. People deny mental health like a myth. It's too scary to look inside and realize the truth that's inside. It's easier to blame others and the world outside of our skin.)

"Your knowledge should be used for the creation of peace, not the creation of a problem.." (I'm not a big fan of should statements but, dang, to stress focusing on outcomes that are meaningful and conducive to life. . . . I like that. Like Einstein!)

". . . for ancient Indian psychology, modern western psychology like kindergarten." (So, I guess even the Dalai Lama says so much about "psychology." Psychology is neither good or bad but depends on how one uses it, like math. It's truth doesn't matter what anyone believes.)

"We must learn about Emotions to work out our destructive emotions. . . . Tackling our destructive emotions is not a religious matter."

"Fuller knowledge about the system of mind is very useful. Very essential."

He very much praises the “system of mind.”