This is the most common thing everyone loves to say whenever anyone says they study any martial art, and they use it as an excuse to study
no martial arts, because "what's the point"
I never suggested that BJJ was going to be the only thing you should learn or know if you wanted to defend yourself in a fight. Cross training with some striking (muay thai, boxing, something) and/or weapons training? Sounds great, go for it.
To be clear: I have been in my fair share of fights, IRL. I've been stabbed twice. I grew up in Brooklyn and spent a lot of time in, well, less reputable bars and clubs. Most fights do not end in the first five seconds, and you should GTFO if you can, at all. Not fighting is the best way to win. If your opponent has friends with them, GTFO at any cost; that goes without saying. Most fights go to the ground, relatively quickly. When they do, taking their back and getting your hooks in is far better than mounting them, since you can absolutely control them from that position while someone else calls 911 and/or finds help to break up the fight you definitely didn't start, because starting fights is the fastest way to lose them.
As for "adrenaline matters" - this is explicitly why you train. It absolutely matters. But someone untrained will just spaz. Maybe they get lucky, maybe they don't; but they usually don't. Someone trained may not remember every single thing they know; but so much of it becomes instinctual that even with the adrenaline dump they are definitely not on their best game, but are still far more capable than the untrained individual. Furthermore, competing helps a lot with desensitizing yourself to the adrenaline dumps.
Also, "before you realize there was a fight about to happen" is not a thing. I have never been 'caught off guard,' because that is not how fights start. Yes, sometimes an idiot will throw a punch at a random person on the street; but that is absolutely not how most fights start. Well before a fight starts, you have already tried defusing the situation and de-escalating, because engaging is a last resort.
But sure, maybe their "friend will just curb stomp you" so you may as well just never try.