I did a bit of research.
Flacco left Pitt after the 2004 season - while Walt Harris was the coach.
While Harris was the coach, Joe played only minutes in 2004 - he only one completion that year. And as we have noted, played behind Tyler Palko, who was a very good college QB. I recall that Coach P loved Tyler and really wanted him at SU - that would have been a nice thing.
I presume that Flacco was drawn to Pitt because Harris was at the time considered a QB guru.
He never actually played for Wannstedt, whose first year was 2005.
So, I don't think one can pin anything on Wanny over the Flacco situation.
But, it is true that he was never able to recruit a solid or effective QB.
Despite that, he still won nine games in 2008 and ten games in 2009 and went to a bowl with seven wins in 2010.
Steve Pederson fired him and has had a circus ever since. Pederson was also the guy who dumped the reference "Pitt" to the chagrin of many Panther fans the first time he was AD for the school. He then left and went west to Nebraska where he fired Frank Solich following a nine win season. He brought in Bill Callahan who drove the program to new lows.
My suggestion for Pitt fans - fire Pederson.