In fact, data suggest that the problems you observed probably would have been worse absent the stimulant medication. A treatment can be beneficial even if it doesn't completely eliminate the associated issues.
Medicine can help, but they're not a silver bullet.
So it could just be that the people you've noticed are just people who are more likely to develop these problems.
And if you want an anecdatum, I have ADHD, unmedicated during most of my childhood, and I went to develop all of the above except for psychosis.
Absolutely, you are correct. To be clear, that's 100% a hunch I just posted, based on no data or experience other than the people I have known that long who are now adults. Funny thing, a lot of them are deciding not to medicate their children.
Moreover, delayed diagnosis ADHD is even _more_ correlated with issues like anxiety than the ADHD population in general. If you think about it, that outcome is predicable: a lifetime of experiencing the kinds of problems created by executive dysfunction (especially with little or no understanding or explanation of the phenomenon) is a perfect breeding ground for anxiety or depression or both.
I'm not sure if the same statement is true for diagnosed but untreated ADHD, but certainly seems plausible.