Are budget Amazon and Walmart mountain bikes good for real trails?

The consensus across specialist communities like r/MTB and r/mountainbiking is that sub-$400 big-box bikes are fine for pavement, fire roads and light trails, but reviewers repeatedly warn they fall apart or feel unsafe when pushed on technical terrain. If you plan to ride genuine singletrack regularly, reviewers steer buyers toward a real hardtail like the Canyon Stoic over a department-store full-suspension bike.