After some consideration I came up with two assumptions, please correct me if I am way off here.
The merkleroot being part of the block information is a validation shortcut?
Difficulty not being part of the block information is due to the fact this can be derrived from the version header? (but this would require to have all difficulties being hardcoded forever into the code? This doesn't rhyme with dynamic difficulty, so basically I am wondering how a block can be validated without seemingly "knowing" its difficulty)