And yes, for beings which are so superior as you make them out to be, or at least cunning and dangerous enough for there to be a special warning given to shadowrunners to not deal with them I would suspect them to succeed more than they currently do.
Do I really need to regurgitate all the explanations that have already been given to you? Dragons succeed all the time. They succeed in private affairs that take place in the shadows, as well as more public ones. They succeed so often that it isn't even worth mentioning most of the time. 'Man bites dog' is front page news, 'dog bites man' is third page news, and 'dog bites chew toy' isn't news at all.
It would be nice if the lore would match up, meaning that if you want to continue to use the "Never deal with a dragon" saying and have dealing with a dragon actually raise notoriety as the rules suggest, that there be an actual in game lore reason as for why dragons are so fearsome apart from nostalgia.
Notoriety has nothing to do with it. Dealing with a dragon is tantamount to entering a white, unmarked van because some creepy-looking guy told you there was free candy inside; you're going to get fucked. I don't understand why this is such a hard concept for you to grasp.
Because in my opinion in the last few years of the metaplot
Newsflash: there's more going on in the world than just the metaplot. Shadowrun is a huge, dynamic world where everyone is always up to something (multiple somethings, even), and you don't get to hear about all of it, period. In fact, you get to hear even less of it when you only pay attention to one plotline. While that one dragon whose name I cannot even be bothered to look up got screwed by the CFD saga, every other great dragon went on advancing their personal agenda and making bank. You know, business as usual.
No, I did not miss your anecdote, but instead of Lung the exact same scenario could have happened with a metahuman triad leader
Lung's actions were the opposite of what you'd expect from a metahuman Triad leader. Triads are families; they are described as taking care of and standing by their own, whereas some other syndicates have no qualms about disposing of spent assets. A metahuman Triad leader would've told the crew to abandon ship or to allow themselves to be arrested without resistance, promising them good lawyers and that their families would be taken care of if they were imprisoned. Lung killed them all because they had failed him, and this is an individual "described as a reclusive and patient dragon who tends to plan and manipulate things in the shadows, slowly spreading his domain rather than taking aggressive actions." Says a lot about the whole species, doesn't it? Meanwhile, he let the two outsiders responsible for the whole mess, the two who actually tried to sabotage one of his enterprises, get away scot-free because he thought they were cool guys. If you don't understand by now why you don't want to deal with dragons.......well, sorry, but Shadowrun isn't the game for you.