“How do you know they weren’t exceptional? Did you read their apps?”
I have known this year’s group since nursery school. I live on the cross walk to 3 districts so I have friends in all 3. The district that does not do well actually did have an extraordinary Valedictorian this year, he was also an EMT, did Siemens, worked many hours to save for college and volunteered with the fire department and does not have parents who are overly educated (they went to college but work ar relatively modest jobs not by choice). He will be going to Vanderbilt, because that was the best he got into. Nice but not where he really wanted to go. The ones who got into the HYPSM this year and last were not anything special beyond stats. One is not even doing well got a C+ this year in college. There is nothing wrong with them, they just do not stand out in any way.
As for luck, I really do believe for many candidates they just went Enie, Menie, Miny, Moe.
However, some of what you mention is more than luck and the reason behind these questions like the OPs. Is there some magic formula. No but research helps. I know I did not do my research properly. I was recently told (DO NOT KNOW IF THIS IS REALLY TRUE):
For example, the Europeon language department at MIT is always underservered. People are not going to MIT to major in French or German. If you can show that you really want to be a French major (and have the ECs, travel or interests), then you might get into MIT with a 3.8 and 33 or 34. You probably would not as a CS major. Same for other schools. For example Penn’s SEAS is toughter to get into than arts and science since it is smaller, if you want a theoretical engineering major you may be better off applying as a physics or chemistry major. May or may not help but that is something that you need to look into. Of course you have to want to major in that. Many people are undecided about majors, they have a general idea but pick something only because the school asks, not realizing those choices are important.