The Greats of L/ROCH were almost ridiculously evenly matched. Nobody really had much of an advantage over anybody else.
If the margin between the Greats' martial arts level was that slim, then ostensibly, one Great getting help from another (non-Great) fighter could turn the fight in this Great's advantage. What's the minimum martial arts level of the interloper, however, that could actually make a difference if this interloper were to help tip the balance in favor of one Great against another?