I'm not sure I'm answering your question but in the GD forum, take a look at the thread that says scouting messages below this one. It shows you the different messages from recruits when you send an assistant or head coach on a scouting trip and how you want to recruit the good potential (or great potential) responses. Those players grow faster than the average and low potential responses. Of course, when a recruit/player sees more playing time, they also will increase faster than a player/recruit that doesn't see the field.
So when you compare your two QBs above, the 70 WE stands out, but only if he has good or great potential. If he has average potential and the WE40 player has good or great potential, then you would go with the WE40. In either case, go with the QB that has good/great potential.