I don't know how you can call him terrible. Here's the numbers - judge for yourself:
http://www.sports-reference.com/cfb/players/matt-mcgloin-1.html
As a RS FR in 2009, he was 0-2 passing. I guess that was terrible. In 2009 he was 118/215 for 1548 yards, 55%, 14 TD's and 9 picks. Terrible? It ain't All-American but playing half the time, I think that's kinda pretty good.
If any year was 'terrible' it would be his JR year, again splitting time with guys who truly WERE terrible:125/231 for 1571 yards, 54%, 8 TD's and 5 INT. With Billy around to actually coach and develop his skills in 2011, McG went 270/446, 3271 yards, 24 TD's and only 5 picks.
So in three years of playing, he had a great year, a good year, and a dull year. By no reasonable estimation, especially since the man was never a full-time starter until 2011, did he have a year that was terrible. What was terrible was the way he was mishandled. I don't criticize Jay's coaching of the other guys nearly as much as I blast him for ignoring a guy who was clearly better and stubbornly insisting that obviously inferior guys should play.