I never ever heard of any bad things Duncan did off the pitch, in fact, that he wouldn't pose for pics when doing his charity stuff made me respect him all the more. Duncan took it to the max on the pitch every time, sometimes his temper got the better of him, sometimes referees were out to get him. Comparing that on field effort and desire to carry the fight in what was sometimes a bit of a spineless team is why we loved him, and when he had his days on top form he was invincible - to Drenthes lack of everything except a few 30 second highlight reel moments against lower opposition is unnerving.
When we were well below average Duncan was a light in the darkness, in the current setup he'd have scored well more. Knocking the big man for me - isn't helping your argument at all.
Drenthe was damaged goods before he arrived, we've seen first hand now why. Consider it a bullet missed.