I believe that YG got it all wrong when he thought that reaching the next level of progression meant that he had to be able to use a wooden sword as if it were the heavy iron sword.
Evidence 1:
YG failed miserably in wielding a normal sword like the heavy iron sword in his fight against the BWM. At that point in time, YG's internal power was already incredibly strong. If he had fell so far short, how much more power would he have needed? Is it even swordsmanship, which DGQB is known for, if reaching the next stage just meant increasing internal power to a godly level?
Evidence 2:
JY said that YG's skills with a sword weren't particularly good. This is the most relevant evidence, imo. Why would JY say that if YG was close to mastery of DGQB's wooden sword stage? How could anyone that's close to mastering DGQB's wooden sword stage not be considered to have particularly good swordsmanship? The only logical answer is that YG was never close to mastering DGQB's wooden sword stage.
Personally, I believe that JY originally did meant for YG's method of training to be the right method for reaching DGQB's level but in later years his more advanced theories of mystical MA had caused him to think differently.
Although there's no direct evidence, I believe that DGQB's later stages can only be reached by having very advanced knowledge of swordplay such as DG9J. In SPW, it was made clear by JY that DG9J was the pinnacle of swordsmanship. Therefore a top swordsman should be someone who has full mastery of DG9J rather than someone who is able to use a wooden sword like it's metal. Because SPW was written after ROCH, I'm more inclined to go with the theories that are presented in SPW.