[D-Machine]

Insofar as they are testing very broken and simple "skills" (as evidenced by comments in this thread), and still find net significant net positives in some cases, negatives in others, and huge variability overall, I actually think this is a fun paper providing support that, at least if you count using skills here, you can, in general, very objectively and quantifiably be holding it right/wrong.

I.e. your use of skills resulting in differences of up to ~52 percentage points (or negative percentage points) in improvements (or degradations) in your percentage pass rate is a decent first-pass measure of the importance of skills here.