There's a mix of difficulty in here, but the main problem is that it's a MIX and not a ramp. Most of the worlds have 7-8 puzzles so tightly constrained that the puzzle ends up being trivial because you only have one sane way to even approach them, 1-2 that are of a good moderate complexity scattered at arbitrary points in the world, and one absolute ballbuster that's usually smack in the middle instead of at the end. There's no real sense of progression.