I agree with you. I have read and watched MY children parent THEIR children. The differences are astounding. The behaviour of my 5 grandchildren when with me or at a family event is excellent - praise wherever we go.
At home though it's a different matter. Belligerent, rude, untidy to the point where the floor cannot be seen for clutter in their rooms and oblivious to the dirt that accumulates.

Mum has
a) told them it's their responsibility and
b) works 12 hour days in a challenging behaviour school - she has had enough when she gets in!
Aged between 12 & 18.

Dad (my son 🙄) doesn't believe in punishment...it has to be 'positive re-enforcement.
Let me tell you - it doesn't work!