Not sure if Huntington had anything to do with that, though. Likely he didn't.
Burnett had a 3 WAR year and then a 4 WAR year as a pirate, not a one year thing and I see no reason why he'd fall off a cliff. Liriano didn't have a fluky season by any stretch, and even his projections have him at about league average (conservative IMO.)
I know he was the guy to s*** on before, but you can't ignore the moves he's made that we all loved. Liriano was a clear buy-low (decent peripherals), Burnett was a buy low (based on his xFIP in 2011, Huntington picked up a buy low player who fit into his home park perfectly), Russell Martin and his underrated D and framing. It's like he became a different man.