The dopamine amphetamine (amphetamine) has specific use-cases, primarily for ADHD, but has issues with abuse potential.
The norepinephrine amphetamine (phentermine) has specific use-cases, primarily for appetite suppression, but has issues with abuse potential.
The serotonin amphetamine (MDMA) might also have specific use-cases, but definitely has issues with abuse potential.
A thought that occurs is that the first two is that they were studied for their use-cases when there were no alternatives. e.g. phentermine might have utility in treating ADHD, but its never been studied because what marginal utility would that have over amphetamines or methylphenidate? If GLP-1 agonists had been discovered and deployed before phentermine, the latter may never have found a clinical indication. What use does MDMA have that isn't already well addressed by other, safer medications? If I had a case of truly treatment resistant PTSD (i.e. failing SRIs, NRIs, DRIs, sympatholytics, buspirone, etc.), why would I use MDMA over an MAOi?