Okay as someone who professionally works with kids, I'll weigh on on this and say: the thing about defiance and "brattiness" is they are defense mechanisms for having no power in your life.
Kids and teens do not have power in their life. Even in the most ideal of circumstances. They can't really make informed choices about voting or houses and especially in America, the entire social structure is hostile to letting them go where they want to go.
So OP is absolutely right and put it beautifully. "it's important that it's your own way." I've seen preverbal babies force their shoes off their feet in response to a completely unrelated obligation because I can force them to take a nap but I can't make them take a nap AND nicely keep their shoes on. It is arguably a pretty stupid defiance, but defiance isn't about being smart.
It's the scream of a person without power insisting if they have no choice but to do this, they will do it their way! And that's more important than practicality. It's more important than being reasonable.
I firmly believe that deep down adults aren't less bratty or defiant than kids are- they're just given more leeway and power so they're more used to having control and use that to cope. The average 30-year-old would absolutely have a meltdown in the pasta aisle if they were regularly dragged to places they didn't want to be by another adult who they were never allowed to be away from or choose where they were going besides very limited exceptions.
(also disclaimer that in using the term "bratty" I am by no means condemning this behavior. It's born of a frustration that is completely understandable.)