Completion percentage is a huge part of determining success at the next level. However, you have to take into consideration certain factors like dropped passes for example. Both Jackson and Rosen had a ton of dropped passes for them. Like you said systems play a huge part in college QBs sucessfulness. Bottom line is if it were as simple as looking at completion percentages, tds, and picks then there would never be a bust in the NFL. It's just not that simple and so many more factors go into scouting QBs.