There is no question that you can get as good of a college experience going to a good flagship (especially in an honors program) as an elite private. It is how the individual grabs his/her opportunities. Frank Bruni’s book is a great read on this.
That having been said, I do think the opportunities offered are different. I seriously considered UD, but if I had gone there, I am pretty sure I would have chosen to be an engineer. I probably also would have likely hung out with my high school friends who ended up going there, and most likely would have ended up working for DuPont, Hercules or some other “science/engineering” company in that part of the country. Instead, I went to an Ivy, and ended up in a career in law and then finance and have lived all over the world.
I also believe that I was likely pushed harder intellectually. You go from a situation of almost always being the smartest kid in the class to someone pretty average, and you see and study with others who are much more accomplished than you are. It is not to say there are not plenty of extremely strong students at state schools, especially honors programs, but I suspect the depth and breadth of the strength is different.
In comparison, my brother went out of state (UofM honors), spent his junior year at Cambridge and went on to med school and is affiliated with one of the top hospitals in his area of specialty. So going to a state school did not limit him in any way. I do think it can make a difference though whether you go in state or OOS. Sometimes in state makes staying in place too easy.
With my 2 kids, they had places in the our state flagship (a good one). We had the luxury that finances did not limit their choices. D had the opportunity to continue to play her sport at the D3 level and attend college in a more intimate LAC environment that suited her personality better than our massive flagship. S was more suited to a larger university, but I am not sure if he would be having the same experience there vs his Ivy. His current suite consists of classmates who have lived in France, Hong Kong, Shanghai, Ghana and Italy. He has spent a summer abroad in an immersive language program, worked a consulting internship at a boutique shop this past summer and is doing a bulge bracket IB internship this summer. I don’t doubt he would have met great and interesting classmates and had good summer work opportunities, but they would not have been the same if he had gone to our flagship.
At the end of the day though it all comes down to optimum fit. I agree that the Ivies or you name it elite school don’t have a monopoly on that.