I think what you say is true. However, I also think that the practice of developing a QB is never going to be supported statistically, very well. Heck, taking QBs high in the draft and having success with them is not a very good bet statistically.
The Cowboys, IMO, should be the standard barer for this practice in the NFL. As an organization, I am not sure if there is another in the History of the NFL who has benefited more from the practice of developing QBs. If you look back through the years, we probably owe more to this practice then anybody else.
Roger Staubach, was not the Franchise when he was drafted. He was developed. Drafted in the 10th Rd in 1964, didn't play in the NFL till 1969, sat behind Craig Morton and went on to be a HOFer.
Danny White, another example of a guy who we brought in and developed. White played for 4 years in the NFL before he was a starter. He never won a Championship for us but he was a pretty darn good QB for us.
Tony Romo, undrafted player. He was developed for 3 years before he ever got a chance to play and now, he's one of the very best QBs in the NFL.
Not trying to single you out but just wanted to get the point across that as a Franchise, we are probably the biggest benefactors of QB development, down through our History.