Yes, I agree. The core of drama is conflict.
It doesn't have to be one's relationship any more than it has to be dramatic eating a sandwich or driving a car.
If there was a way to bring conflict to those things, then they can be drama. Someone almost chokes to death eating a sandwich. Driving a car is often used in drama - the car chase. Or it could be a car race. Stealing a car. Driving a DeLorean that's also a time machine. The possibilities abound.
The topic doesn't matter. Invest it with conflict, and it's drama.
Just put the dramatic focus on something else and let the happy, functional relationship just be an element of the show.
Then the relationship isn't what the story is about. That's okay if you'd rather the story be about almost choking to death on a sandwich or the DeLorean time machine, but then it's misleading to say that the relationship is the point of the story at all. If there's no conflict in the relationship, it will be shoved to the background. It might as well not exist in the story at all.
I'm sure what Ball means is,
if you are writing a story about relationships, there damn well better be conflict in those relationships. If you are not writing a story about relationships, why are you bothering to put a relationship into the story? Maybe it's so that when the guy almost chokes to death on the sandwich, he thinks about how much he'll miss his wife and kids.
There's no conflict between him and his family, but the family exists because it amps the conflict with the sandwich. If the family has no role in the drama at all, the family should end up on the cutting room floor.
And who says happy, functional people having to deal with sudden life situations has to be boring?
Then the point of the story is not their relationship. It is whatever external element is bedeviling them - not being able to make the mortgage for instance. Bad kids, bad job, whatever.
Elements in stories - relationships, sandwiches, cars - earn their place in the story by helping to amp the conflict and therefore the drama. If they don't contribute, they should be edited out.