Even cocaine and amphetamine are apples and oranges, despite both being classified as stimulants.
Anyway, it's basically that stimulants prevent falling asleep, passing out, or (ideally) dying at high depressant doses. Which allows users to experience more intense effects from said depressants. And that depressants reduce anxiety, relax, and (ideally) prevent dying (usually from cardiac arrest) at high stimulant doses. Which allows users to experience more intense effects from said stimulants.
And re cocaine vs methamphetamine, I've used both a lot, albeit many years ago. And sure, they're quite different. But they both made me happy, and kept me awake. As I recall, cocaine was much better for play, dancing, and sex. And methamphetamine was better for working, driving, and just slogging through emergency situations.
For a few years, I basically lived out of a bicycle, and I always carried methamphetamine and morphine, in case of emergencies. It was standard issue for most all military services, so hey.
John Belushi, Chris Farley, Pete Farndon, Mitch Hedberg, Philip Seymour Hoffman, Brent Mydland, River Phoenix, Eric Show, Layne Staley