What makes it 6MSJ though?
JMZ couldn't quite keep up with DY's firing rate but DY also had significantly stronger internal energy. Not to mention JMZ had already engaged in a fight without a break before this and had a gash on his body that's still bleeding out.
In the very quote we both posted it says that JMZ felt that DY's internal energy "was only growing stronger and stronger" and that DY's techniques were "boundless without fathom, as though creating new stances on the spot".
JY clearly explains that the latter was not true at all leaving only the second half the part with relevance.
Thus DY's internal energy allowing him to pour out attacks with power was what JMZ ultimately fell to in this case.
Let's say DY had learned Flaming Saber Palm instead of 6MSJ. Again he won't know the techniques but he'll have the saber chi portion down. We know that it's possible to fire multiple blade at once with this skill as well. Is there any reason to believe that DY doing a machine gun with FSP would not also wear down JMZ?