The further off something sits, the less it weighs on today's decision. That is not a flaw in your reasoning. It is how the weighing works for everybody.

What the research says

A meta analytic review confirmed that children and adolescents with ADHD show more reward delay impulsivity, preferring a smaller reward now over a larger one later, a form of impulsivity studied less than quick responding. A separate case control study found that difficulty with waiting contributed to ADHD independently of executive dysfunction, variable reaction times and emotional difficulties, so it is not simply a by product of poor executive control. Both are group comparisons, describing a tendency rather than predicting any one decision.

Strength of evidence: one line of research. A single study, or a theoretical account.