My son was a big fish in a small pond school (uni) and he benefitted trremendously. Yes, he was always at the top of his classes (and frankly didn’t have a lot of competition for that spot), but he was also noticed and this helped him get a spot in his uni’s grad school with a grad assistantship, so he got his first graduate degree this way (the GA covered all of his tuition). By the end of that degree, the school hired him for a full time position and then he went on to earn a second graduate degree (free tuition is a benefit of working at this uni) and his wife also was also able to get her MBA here (since spouses can also receive free tuition).
My daughter also ended up at this school but studied a completely different discipline. She also was a big fish and again, she was noticed by her teachers and the support staff. As a result, several opportunities for jobs and scholarship applications came her way - a seriously nice perk.
So while this uni isn’t very selective, it was a great place for my kids as they were able to shine there.