That's a great point.
Even in Terror of the Autons
when the Doctor is warned by the well-attired Time Lord about the Master, the Doctor was clearly familiar with him, but considered him to be fairly harmless. I wonder if the original intent was for the Master to be a more deadly incarnation of the Monk? Based on the Third Doctor's initial assessment, it would follow.
Of course, I do NOT think that the Monk was the Master.