Most parents canidentify with and sympathize with a frazzled parent trying their best, but if a parent refuses to deal with or flat ignore their child’s behavior that’s a problem.
Yup. Being a parent requires loving your children and teaching them how to behave in public. Some parents can do that, some won’t. Social pressure works on most of the latter.
The fact that both the parents and complainer were in business class indicates that both sets have money and both sets see themselves as entitled. Likely indicates that both sets are unlikely to seek the middle ground.