I agree with pigsonthewing.
Baron Miles was 5'8" and an awesome corner. Size is important, but not everything. Grixby got beat several times last year because he was matched up with the opponents' #1 receiver game in and game out. Why? Because he was the best corner that there was! If you get a chance to, watch some of last season's games again and really watch Grixby. He made some damn fine plays and played solid in run support defense. Jones got schooled last year way too much going against top receivers(see Sweed running past him for a TD and Jarrett making him look absolutely silly). With that said, I think Jones ends up having a fine season this year due to his trials and tribulations last year.
I think that stating Thenarse should have started based on his athletic ability is a misled statement. Yeah, Thenarse would have had it rough and improved, but how many close games would he have cost the teams? If you think Callahan's hide is on the line for going 9-5, what do you think a 7-6 or 6-6 season would have done? KU and A&M could have been different stories with just 2 misplays by an inexperienced corner.
as you were typing this, i was lookin up barron miles Stats and receivers that he locked down. lol you da man! Guess how much Barron Miles weighed? 160. one-friggin-sixty. but the difference between Grixby and Miles? Miles had safeties and a couple of backups.
Safeties may be a contributing factor, but the real difference between Grixby and Miles is talent. You are correct about the size of NFL corners, being shorter gives you a lower center of gravity and helps you react to a WR and change directions with him. BUT! You need to also have the ability and a knack for it, being short, fast, and experienced doesnt make you good. Thats why I'm not a Grixby fan, I respect his work ethic and attitude, but I dont think he is at the level we need him to be to compete on a national level.