The "it" feeling only goes so far. And in fact it only means anything at all if the player in question has transferable skills and physical attributes. Many guys were tagged as having "it" in the college game (and indeed Europe) - Adam Morrison being a prime example. That's why you cannot rely solely on what you see at the college level and at face value. You absolutely HAVE to look deeper than that to get a good read on a guy.
You could easily argue that Luke Harangoody has "it". In most of the games I've seen he appears to have it. Outplays better and bigger prospects. Has a fiery drive. Rebounds, scores. Yet despite what he actually does, and despite his (relative) domination, my head over-rules my gut and tells me that he's not going to be a difference-maker on the next level. Of course, I could be wrong, but I sincerely doubt it. Without blowing my own trumper, I think I'm pretty good at evaluating young talent. Harangoody, at best, will be an energy-provider in limited minutes.
Looking at athletic ability, background, character, measurements etc., they all can be valuable. I'm not saying they're more important than games, but they are important. Watching our very own Tyreke Evans last year, I wasn't sure exactly what he'd be like in the Pros. The dribble-drive offense looked awful, he consistently drove into traffic and took poor shots. He was trigger happy from the outside. He made some poor decisions with the ball. Yet if you looked past that, looked at his physical dominance, his size and power, his family structure, his ability to put the ball on the floor, get to the hoop, defend and rebound, you could see that this clearly was a guy who could become something much more than his college play indicated. And that's how it turned out. In his first year in the NBA, in a much MUCH better league, Evans far out-performed himself from the preceding year. Who would have guessed it? BTW, not many at all said Tyreke "had it" last year. In fact, I think you'll struggle to find anyone who said he "has it" before we drafted him, expert or not. There were too many unknowns about how his game would translate. Obviously all those questions have been answered now.
It's reasons such as this that you simply CANNOT simply rely on the visual evidence that takes place on the court. You can't. Too many variables. Too many things unsure. You have to look past that. Anyone making decisions based purely on their gut simply isn't going to be right too much of the time.
Analysis is quite important. It allows you to break down each part of a players game - his weaknesses and his strengths. Things that are often over-shadowed by a more prominent facet of skills in college. Things that could be absolutely detrimental to a young guy's chances of getting PT at the next level. Things that you might never notice unless you actively looked out for it during a game (which isn't going to happen if you want a read on all aspects of a players ability).
I agree with you about comparisons. They are the least relevant part of the whole draft build-up. I guess people just need to put a tag on players. I remember people were comparing Tyreke to Larry Hughes last year, even though that comparison never really had too much behind it. Of course, people inevitably linked Tyreke to laziness and injuries and being over-paid. It's certainly the silliest part of it, and rarely are they right to any significant degree.
As for Hayward, I've seen very little of him. Which may make the following somewhat of a gamble, but I'll bet you a signature of your (and mine) choice that Johnson will be a far better player than Hayward down the line. Might have to wait a couple years for us to find out the result, but I'll still be around. Unless of course you weren't saying Hayward will be better. In which case, I retract my bet.