I'm confused. Caffeine is a stimulant. It may be weak, but it's definitely psychoactive. I am quite sensitive to it actually, and even lower dosages produce euphoria and fairly pronounced stimulation. I wouldn't call myself completely sober after I've drunk a strong coffee; my thinking may not be as impaired as with alcohol, but it's no less impaired than with weak opioids. Coffee also sometimes gives me a stoned high, which I've been wondering about - why? This is why I don't drink it that often.
It's kind of funny actually, because my ex is sensitive to it as well. She's a very active and energetic person in general, but on caffeine she just goes completely nuts bouncing off walls. She decided she had to abstain from coffee for that reason, and I'm not even joking. Of course, this is just a few people, everyone's different. Just saying that it may not be prevalent, but it's definitely possible.
My point is, again, that you just have to keep an open mind about it and decide on a case by case basis. There's no one-size-fits-all way to define it. My ex is definitely not sober on caffeine, but it doesn't mean anyone who takes it isn't. Most are. You probably are. It's just not as black and white as we sometimes make it out to be.