That's a good question and one I've been thinking about as well.
Would be awesome to develop a framework for rating blues and blue/rock songs in terms of degree of difficulty, or mapping to Griff's lesson content. Easy to say, and I imagine very hard to do as it's so subjective.
I do recall a blog post years ago where he did this,
https://bluesguitarunleashed.com/blog/some-recipes-for-blues-songs/
Justin Sandercoe at JustinGuitar has made an attempt at this, and it's pretty good. He's got a couple of hundred songs that he's featured, and taught on his site and you can sort them by 9 different degrees of difficulty. He also maps some of the songs to his lessons, whereby some songs are from his beginner series and are rated as beginner songs. What also helps is that he'll separates some of the solos as they might be at a more advanced level than the song. Eg. Crossroads.
He covers a lot of the genres, so you have to know what you want, and what you don't
Fender Play has tried to do something similar, but you need to pony up some $$'s to see the good stuff.
It's mostly oriented to beginners though, and covers a lot of genres.
Other than that I not aware that there's any song ranking within the blues, or blues-rock space.
Does that help?