I don't know what the context is for Stafford's first 5 years, but you can't just determine the worth of a QB on stats alone. He is one player on a team of 53. Important yes. But everything but the presence or lack of a good running game, WRs, Oline, and D have to be factored in. And the chicken and egg problem factors in as well. That's what GMs and HCs are there to determine.
I'm not drawing conclusions. I'm saying that a QB's TDs and INTs are but one of many factors that determines what's important: wins and championships. All the rest is for Fantasy Football and maybe a FA getting a big contract.