Yes, they definitely should not be infused with the dark will and should be less than the Seven Deadly Lords. And I like the good Doctor's idea. I can sort of see a Darth Vader thing going on. Lust says, "Sadism... you have failed me for the last time. Next candidate!"
And maybe not call them Lords of X... maybe a different title, like "Duke of Sadism," or something similar but more cool.