I think you touched on pretty much every "advantage" the returned Mormon missionary runners have. I wouldn't discount any of them, 1-6. I grew up in Utah myself and went on a church mission. But there are two extreme disadvantages that make great Mormon runners like Ed Eyestone, Henry Marsh, Doug Padilla and others who served LDS (Mormon) Church missions special.
First, on a two-year LDS mission, it is extremely hard, if not impossible to maintain good running condition. Missionaries are forbidden to go anywhere without their missionary companion, another young man (or woman, for female missionaries) with whom they are assigned. They must be together 24/7. This requirement has safety, accountability, and even "spiritual" reasons that I won't get into here. When I went on an LDS mission, I was in great running shape, and I gave up an athletic scholarship to go. I hoped I would somehow be able to maintain my fitness AND fullfill my church obligation, but it really was impossible. Missionaries get up at 5:30 or 6:00 a.m. and prepare for the day. That includes scripture study, lesson review, and planning. To go running in the morning would require that you get your missionary companion to go with you even earlier, something that worked just once for me. Then, after scripture study, you spend ALL DAY walking from door to door proselytizing and teaching lessons to anyone who will listen. You may get to your "tracting" location by bicycle, but mostly it's just a whole lot of walking. So you're on your feet a good part of the day, but it isn't running or even walking fast. Meanwhile, church members invite missionaries for dinner quite often, and they are happy to stuff you with food, leading to most missionaries putting on some weight for their two year mission. Church members know that missionaries are dirt poor, many of them paying for their own missions are having their parents pay for them. So without those "dinner appointments" with Church members, most missionaries eat lousy, unhealthy food. Thank heavens for church members, though, because they're happy to fatten you up. Bad combination for runners: little or no running, and putting on weight. You get half a day off each week, but that's for doing laundry, shopping for food, etc. Then it's right back to missionary work.
Second, there is a strange thing that happens on a two-year church mission: those missionaries--well, almost all of them--find new priorities in life. Their priorities, which are drilled into them constantly, are that you should serve an honorable mission and then marry a good Mormon girl and immediately start a family. If you come back from your mission and are even remotely attractive--and sometimes even if you aren't--you have a big flock of young Mormon women whose biggest priority is finding a returned missionary to marry and make the father of their children. But when you meet one of these exemplary young women, you can't do what hormone-filled young men and young women naturally want to do because that's forbidden until after marriage. Talk about added stress, along with the social stress, to get married young! It worked on me that way, and one year after we were married, along came our first child. The point is that SO many potentially great Mormon runners who serve church missions NEVER get back to where they were in running before their missions. Your priorites change. Two years away from running, while you concentrate your whole life on teaching people about your church will do that to you.
The amazing thing is that there have been some truly great former Mormon missionaries, including those I named above, who have somehow come back and actually lived up to their potential. It's not just physical maturity (age 22-26 rather than the typical age 17-22) healthy lifestyle, altitude and good coaching. Ed Eyestone would probably tell you the same thing. It's whether a young man really wants it once they return from a mission, and whether they get enough support--from spouses, especially, when they get married so quickly--to pursue those previous high school dreams. Remember that most of these returned missionaries come back without an athletic scholarship and have to make team, too.
I was never as talented as Eyestone, who was a grade ahead of me, but still I deeply regret not pursuing my own running dreams. It's all water long gone under the bridge, but I'm not alone. There are many, many talented Utah Mormon high school runners who will never reach their potential. But when you really think about it, should running ever come before a wife and kids? And is being able to get from point A to point B faster than other people really so important in the grand scheme of things? To meet more important priorities while STILL reaching your running potential . . . now THAT'S an admirable feat in my book.