People here obvouisly did not watch a lot of Tampa Bay football if they thought Glennon should be handed the starter spot. He was not good last year. Tampa had the 3rd worst offense in football and was dead last in passing yards despite playing in an offense that had some decent pieces on it including on the of best mid/deep ball WR's in the game in Jackson.
Glennon's stats hold up to quick eye ball test overall only because of the conservative approach Tampa took early in games. When they eventually fell behind and had to rely on the passing game to put points on the board, Glennon was flat out awful. That alone is what cost him his job. He fell apart almost all the time as the game wore on and more and more was asked of him.
On paper Jackson and McCown look like a match made in heaven with how McCown was able to utilize Jeffries last year. Jackson wont make the same amount of jaw-dropping amazing catches that Jeffries made last year but at least McCown is going to give him the chance to make some of those catches.
Not saying Glennon should be a thrown away or anything but what he showed last year makes it look really unlikely that he will eventually be an average starter for anyone.