Argument 2 (Gelfert: straightforward translation)
"Stylistically, the two [Shakespeare and Marlowe] are as far apart as Beethoven and Mozart in music and like Schiller and Goethe in the German literature"
This assessment is problematic. Whether Gelfert has estimated the range of Beethoven's music ? (between his op.1 and op 135)? - Op.1 is still in great proximity to Mozart. According to Gelferts arguments Shakespeare's work such as "Titus Andronicus" in terms of both style and content is much further removed from Shakespeare's "Macbeth" than the virtually congruent pieces of Edward II (Marlowe) and Richard III (Shakespeare).
The thesis of the book of Conrad is: Marlowe's works are early works, Shakespeare's work are Marlowes late works under the pseudonyme Shake-speare of a real masking person with that Name.-- Shakespeare, of the same age than Marlowe, only began to exist after Marlowe was stabbed. Both overlapped in their literary activity not a single day!
It has been encouraging that Gelfert seems at least to put Marlowe on the same level as Shakespeare's Genius. That's a viable starting-point, which would not have been possible a few decades ago.