Hey, yeah you're totally on point. There's no scale. It's just informative and neutral throughout.
You shouldn't be reading RC passages thinking that every passage has a Scale. Most do, but it still might only be like 70% of them.
So don't try to force a square peg in a round hole.
EVERY passage has an author, who had a specific purpose and, through the lens of that purpose, could be said to have had some main point.
But this passage is a challenge even when it comes to localizing one claim as the Main Point. It was really just a debriefing on what corridos are / where they were used. You'd try to find whatever 2 or 3 things about corridos seemed to have the most importance/distinction to the author (P2's notion that they are simple retellings of stories and P3's notion that they use standard conventions)