I will always give more credence to the opinion of someone who has actually seen a kid live (multiple times) than someone's who watched a few minutes of highlight film and claims to be an expert. I will also point out that one of Michigan's mods/writers (from a non-rivals site) actually agreed with you...at one point.
He went out and saw the regular season game against whichever school it was they ended up meeting for a second time in the state finals. He came away a bit underwhelmed. However, he went out a second time (later that season) and said he saw what others were saying about the kid. But that doesn't just dismiss what he saw the first time. So as he looked at more game film (and talked to coaches) he saw that there were times McCaffrey looked like he was trying to win games all by himself and when doing so made mistakes. When McCaffrey played within the position, the system and (looked like) he trusted the other 10 on the field with him he looked electric and special.
The other thing this person noticed is McCaffrey's tendency to press seemed to decrease as the season went on. Thus it looked like it was starting to be coached out of him. That's what good coaches do and I think when it comes to QB coaches Harbaugh's reputation is earned.