He is average and that is being kind. 
Pretty sure Rance and Grimes both have him covered. Plus I think we have some pretty decent kids coming through in McIntosh Short and Marcov that will be good hard defenders over the next few years. 
We don't need to be trading for HBF types IMO.
It was stupid enough last year to trade away two second rounders for a HBF in Yarran. 
To compound it by trading for the exact same type again shows Hartley, Richardson and Hardwick should go now.
Williams 23 yo  181cm  80kg HBF
We only have EIGHT for the two (HBF/Pocket) spots
Houli 28  181  83
Hunt  26  184  78
Yarran 26  !80 83
C Ellis  20  184  75
Drummond  21  182  80
Castagna  21  181 78
Butler  20  182  80
Short  20  177  72
Forget looking for:
Rucks - we have Hampson.
Key Forward - Riewoldt and Griffith for the two spots
Key Backs - Rance and Astbury for the two spots.
We have NO spares for the key spots but we are going to trade for ANOTHER small flanker to add to the eight we have?