The one time I used the method of only scouting all three attributes for 1st rounders, I missed on a couple/few picks, including one day-one pick. That basically never happens to the HUM if you scout all three attributes, but it does happen to the CPU, so it seems to make drafting more realistic and balanced.
I mean, it sucks when you draft a guy and get hit with a player who will be lucky to ever crack the starting lineup, much less make it off the practice squad, but 1st round busts are pretty common, and busts are all the more common in later rounds.
I think if they made it as hard as it is IRL to land good talent in the draft, people wouldn't think the game fun. I mean, how fun would it be to have the Raiders' drafts for the era between their last 2 playoff appearances? I think it would be great, personally, but I think most Madden players would not.