Defending Groton a bit here.
The grind at any highly academic boarding school is very much dictated by how much a student wants to challenge themself. Number of honors classes taken; how serious one is about athletics while simultaneously taking the most rigorous courses offered; and one’s involvement in leadership positions and passion project ECs.
Groton attracts some of the most driven academic students, and the school’s workload correlates to this. However, if one chooses to take easier classes, the workload drops. It’s like this at peer schools as well.