Chavis is pretty awful versus spread O's.
I get what you're saying, and I don't think Chavis is a guru at defending the spread; but he is a very good defensive coach and has had success against the spread. So, I find your comment a bit too strong.
I see Oregon & A&M are the recent examples being used, so...
Yes, we gave up 27 to Oregon last year... but this is the lowest point total anyone held Oregon to last year. After the LSU game, the next best was Washington & USC who held them to 34-35 point-- and after that, nobody held them under 40. So, I would say Chavis did a good-- if not great-- job. LINK
Texas A&M: this past year, only LSU and UF held them under 20 point. Bama was next best at 29 point. So, again, quite good-- if not great. And I think LSU was the only the only one to keep Johnny M. out of the endzone. LINK
Sure, Chavis has had a few memorably bad games/gameplans, but I think the offense may have been a bigger problem in most-- if not all-- of them. And what coach hasn't had bad games? Saban lost to Utah a couple years back in a BCS game, to A&M this year, to a Louisiana directional school a few years back, etc. Pete Carroll lost to Stanford in 2007 when Stanford sucked, etc.
I'm not saying any NFL DCs have Chavis on speed dial for advice, but he's a very good defensive coach and is not "awful" against the spread.
I suppose it's the nature of The Rant to magnify things and turn people into caricatures: if something or someone is good, it becomes hard to imagine how LSU ever loses; if something or someone is less than perfect, that flaw or off day becomes magnified to epic proportions and is never forgotten.