What the hooey is “happiness,” anyway? You take interesting classes, make interesting friends, try new experiences, grow. You can do that at a competitive college.
What you can’t easily overcome is flat-out mismatch (wrong college for you, or inaccessible admins, advisors, competition to successfully register for courses you want and need, limited activities, and then the rest about dorms, food and other personal prefs.)
And you don’t need to have attended to realize the breadth of reactions out there.
Anyway, though the title says cutthroat, OP asked about academic intensity. To me, that isn’t about student competition, but the nature of the courses. Expect any top rated college to have depts that include intense courses and, sometimes, difficult grading.
Lol, you can grow from that. Some kids choose their collees for this run for their energies.
Not all kids are"happy" at Brown, Rice, or Vandy.