I think this is true to a degree, but I think it depends more on where you go to high school.
I went to a high school where less than half the kids went directly to college from my class. A lot joined the military and others when into agriculture (we had a big ag program at our high school) and trades.
So for me, any college would have been “iron sharpening iron.”
Then, I think it’s the demographics of the college too. If you go to a party or big school, that can be hard if you are someone who cannot focus on academics with lots of distractions.
I feel that “iron sharpening iron” is more about picking the school that is the right fit for the individual and less about the school itself. Afterall, while some might thrive at large Ivy’s like Harvard, UPenn or Columbia, others might thrive at smaller college like Bryn Mawr College or Mount St Mary’s University.
And, just because a kid thrives at an Ivy like Brown doesn’t automatically mean that he/she would thrive at Harvard, Penn, Columbia or Yale.
All colleges are different, even inside the Ivy League