You are correct. Common may ask for more than the school does. Let’s say you do ten apps. It will actually show you, this section is required by seven of the schools.
I don’t think there’s any evidence a school answers direct apps quicker. There are some that answer quickly period - like Iowa State. When my son applied to Bama, they weren’t on common and he heard in a week. Some, like I mentioned UMN (at the time) and School of Mines had their own apps or you could use common. But what they did was marketing - they said here’s our app - it’s short - no this required or that required but you can do for better merit consideration. Basically they saw certain kids that are high stats and knew they would accept them - so to get them they would mail this mini app. Perhaps those answer quicker. Those were targeted to high stat kids, likely in wealthy areas. It was a gimmick. Mine used common for them - if you have more info to share already done, why use the gimmick app?
Most high end schools answer based on pre established timelines.
You say you wouldn’t do less apps and every situation is different. But on average, kids absolutely will. They strain with common to do x schools. The average kid will do less without.
And you missed the LOR part. It’s hard to get teachers to do an LOR. Now if you are asking them to do it 8 or 10 times, you are impacting them and they might simply decline.
You see common as impersonal. You know what the school sees?
Identical info.
Why - common shares with them the info they want and excludes what they don’t. And then there’s the school specific info, tailored to each school.
Your student’s choice - but I think your hypothesis is all wrong.
In the end, most schools need the students more than the students need them.
Good luck whatever you decide but your kids will have school work, clubs and more.
Applying with common is stressful.
If kids applied to ten or 15 on their own, I couldn’t imagine. The LOR part alone makes common the way to go.
I don’t know the level of schools you are applying - but looking at some top schools:
Vandy - common or coalition
Wesleyan - common or coalition
Rice - common app
Colgate - Common, Coalition
Bowdoin - Common, Coalition
that’s the first five I picked all top schools. You will likely find many schools don’t have their own app - as these five apparently don’t. But the apps they use include everything they want in their specific sections
Depending on your school list, you may not have a say in the matter.
Good luck