As someone diagnosed in adulthood with both Autism and ADHD (type B - inattentive), I believe you are partly right. Yes, many people have 'traits', because all of the traits of many ND conditions are - simply - traits of being human.
However the prevalence of these traits over time from childhood into adulthood and the pervasive impact that these have on your life are where the diagnostic side comes into play.
As a previous poster stated, on the outside I look like a perfectly functional adult. I have a degree. I am successful in my career, I hold down a relationship, I pay a mortgage and raise 3 children. But what I look like and what I am are two very different things.
It's not as simple as 'I need a calendar to keep track of appointments' - it's needing multiple reminders and alarms for things and still missing them or being late because I cannot simply 'will' my brain into getting going, especially is the appointment is in the middle of the day.
It's having a chair covered in piles of clothes because the act of 'doing the laundry' is actually an umbrella term for a whole sequence of tasks which eats up more mental energy than I can spare on some days and can leave me sat in a heap on the bedroom floor sobbing into a cardigan because I feel like I'm failing at life.
It's not being able to sleep because my thoughts never - and I mean, never - stop racing... from the second I am conscious in the morning (usually at around 3am) my mind is flooded with replays and analyses of every conversation I have ever had, plans and practise runs of every interaction I am likely to have in the coming day, plus the constant whirlwind of all the things I know I need to get done, panic about whether I have enough time to get them all done and the shame and guilt of all the things from previous days lists that I didn't manage and have now carried over, leaving me with an ever-growing insurmountable to-do list.
When combined with my autism (the diagnosis I first associated with) my life is a constant fight between a desperate need and craving for structure and routine but an actual life where I spend all my energy planning and then have nothing left to carry out.
This obviously only relates to my struggles with executive function and does not even touch on my myriad of sensory issues and social/communication differences. Which are a whole other essay in their own right.