Scouts only use PA to assess a player' ability. The snag is that this says overall what value a player has, not what value he has in a certain position.
For example, there may be a striker that has 20 for pace, composure, off-the-ball, finishing and technique who has all other stats of 1. The scout will probably say he isn't much good.
Whereas a striker with 1 in the vital areas but 20s for everything else would probably be rated better (of course he'd really be a defender in that case

).
Scouts also ignore current form.
Find the L1 top scorers and request reports on them - they'll probably say the player would struggle in L2 and isn't anywhere near as good as the goal-shy muppet that's running around up front for your team.
It can be very frustrating. Especially when a scout says good things about a player with seemingly rubbish stats.
When predicting the future, you just can't tell what areas a player's improvement is going to be in.