Parenting books/courses/ training/ anything that promotes good ideas to help a parent having difficulty in managing their dc's behaviour are all good things as without doubt some dc are more challenging than others.
But it is also true that some parents make the situation worse. I have a very well educated friend who woud prefer to label her ds rather then face up to the fact she is overindulgent, has no boundaries with him and won't let her ds know she is upset with his behaviour because she doesn't want him to experience anymore shouting or 'bad vibes' since leaving her abusive ex (ds' father.)
Some mothers yell obscenities at their dc in the supermarket and cuff them round the ear when their dc copy the mother's behaviour..the list of possibilities to judge others parenting styles is endless.
It could be argued that the worst cases are when the dc's unacceptable behaviour is seen as acceptable or provokes no response by the parent. But then we don't know their background..whether it's a matter of 'picking their battles' or ignoring for an easy life.
Certainy there are some harrowing examples on MN where parents are at the end of their tether where the dc swear, spit, kick and hit and tear chunks off walls. Others where this is normal behaviour from their dc.
There is no 'normal' it seems.
When it comes to fussy eaters, how would that child cope in a developing country where there were no other choice but to eat what was on offer? There are no recorded cases there so it does seem very much to be a first world (psychological) problem, like so many of the issues parents/dc face.
I think the biggest problems come from parents who spoil their dc and skivvy after their every need. These parents don't expect their dc to be kind, considerate of others or helpful to others or around the house.
These dc grow up to be self entitled, selfish and expect others to clean and tidy up after them and are often very short tempered when not getting their own way.
Boarding schools, independent schools and state schools all have these types of dc and it's often the parent who laments that the child wanted for nothing and then they are shocked their dc turn into such monsters.