fenway,
In some ways I could make a good argument that velocity is not only in the top 3, but it is a proven #1 with everything else being a distant second. This would not be based on winning or what really is most important, it would be based on the Major League draft every year.
We all know that it is possible for mid, even low 80s pitchers to be successful at nearly ant level. However, I would challenge anyone to give me a name of a low to mid 80s high school pitcher (no matter how good he might be) who has been drafted in any early round.
For sure Major League organizations want the very best pitchers and spend millions trying to get them. In nearly every case, this search ends up with the high velocity guys being selected first. We simply have to follow the draft to find this out.
We all know that velocity by itself is not enough. However, it is still far above things like location and movement when it comes to the draft. Great location won't make someone an early pick, great movement won't make someone an early pick. Great velocity will get a pitcher drafted and only then will things like other pitches, location and movement dictate just how high the pitcher is drafted. I've seen kids who have trouble throwing strikes go in the first few rounds.
Colleges would look at this a bit differently, but not as much as one might think. Google Jason Neighborgall or Colt Griffin.
Both those pitchers would have been very successful if they excelled at location. They didn't! But they were drafted long before those who became much more successful. Sometimes those high velocity guys are Zach Greinke or Justin Verlander. Sometimes they become Jason Neighborgall or Colt Griffin. The only thing they all share is the ability to light up a radar gun. Then the other things separate them.