As someone who was in equivalent programs in the US, I can tell you my experience was that most people in the normal classes didn’t really care, and that attitude is far more likely to discourage the 2-3 gifted students than it is for gifted students to somehow lift up all the other students.
As others have said, gifted students weren’t just smarter students, they were mostly the students who cared.
Calling @treis who claimed[0] 4 days ago that "Nobody is talking about forcing the high achievers to do the teacher's job". Well, here ya go.