Even if luck/genes whatever you want to call it plays a big role, parenting does have an impact too. It is disingenuous to say it has no role. That doesn't mean there is only 1 precise way to parent which results in children turning out well. The can be a number of methods to achieve good outcomes and as some have said they have used different methods with each of their children, because to achieve good outcomes with a more 'spiritied' child might need a very different approach to one who is naturally very compliant. As has been said, what often makes these different methods work within one family is a clear sense of values which underpin it all. Different methods but with some kind of thought out idea and crucially consistent application of it to any one child is vital.
I dont think anyone would argue that inconsistent parenting helps any child. However, you see it all over the place. You see the parent who in public is demanding a certain behaviour from their child, which the child is bewildered by and and doesn't adhere to, because clearly at other times, there isn't the requirement to behave like this - there is inconsistency and what makes it even worse is when parents then get cross and shout at the child, when the child is totally confused by changing expectations.
Surely no one would also think that a lack of follow-through helps children regardless of their personality? Saying that if they do X, then Y will happen, with no intention to do Y and never doing it, just doesn't help any children. But again, it is rife and we will all be guilty of it at certain times - because carrying through involves effort and often sacrifice for ourselves as well as the child, as we too often take an easy route out. So it's not about having loads and loads of rules and threats, but picking which battles are worth the fight and carrying through.
And I agree that when you see families with well behaved, delightful children, although they might have been lucky personalities to start with, there has always been good parental input too. That's not to say that those who are more difficult have had bad parenting. However I don't think children naturally start off knowing about things like sharing and being kind and considering others. Toddlers in particular are often selfish and inconsiderate - it's part of being a toddler, but they can learn to become kind and considerate of others by the time they go to school if parents consistently teach them. Allowing them as toddlers to hit or run around in public places where adults are enjoying a meal or to snatch or speak rudely without being picked up on the behaviours results in school age children who are still selfish and unaware of others, and then teenagers who can be the same. And I guess we all know a few adults who are still a bit like it too.
Some parents clearly have a much harder job. Some children have different needs and challenges or personalities. Some of these cannot be significantly altered by parenting, although even then I believe the values of parents, expressed to their children are understood at least on some level. With most children, parenting makes a significant difference even if it doesn't result in the 'perfect' child whatever that is, and those that say it's totally down to luck, I think abdicate responsibility or fail to realise the real privilege actually that parenting is.