Most scholars state Luther was arbitrary and capricious in his “Distinctions”. The audacity of Luther to subjectively promulgate his negative estimates of the apostolicity of bible books is astonishing and clearly demonstrates his depression and quest for power. It would go well for you to read serious historians on this subject.
“Most scholars”? “Serious historians”?
His thoughts were in line with other scholars of the age. The Apostolic authorship of James, Jude, and Hebrews were and are questioned still. His forwards speak for themselves - both in his favor, and against.
He was not being arbitrary or capricious. Perhaps you should try reading scholars with less bias...or just try reading Luther himself.