That's the entire point I'm trying to make. "Everyone has X" is a categorically wrong understanding of what the underlying problem is.

An equivalent is saying everyone has trouble walking sometimes when we're talking about someone who limps and needs a cane.

The symptoms are not the disorder and don't come from the same mechanism that causes normal people to have difficultly paying attention sometimes.

Absolutely this. A normal range of feeling / experience isn't a "bit of a disorder" ... it is no disorder.

Feeling like you need to wash dirt off your hands before eating isn't a "bit of OCD", that's normal.

Worrying irrationally so much about clean hands that it ruins your life, leaving you crying from normal tasks like cooking ... every touch of a surface triggers fight/flight ... is a disorder.

It isn't the mechanism that's important, but the impact and motivators.

Same with ADHD. A bit of being inattentive or forgetful or whatever ... isn't a "bit" of the disorder that also contains some of those behaviours in extreme.

In many cases it is not a differing underlying cause but simply the same thing further out of balance. Psychiatry diagnoses are essentially never based on a mechanistic explanation and I challenge you to come up with an actual binary change present in those with adhd and those without besides the latter having somebody put that label on them.