Protection rackets are so a thing. In fact, a majority of the mafia's income is based on extortion, loansharking and illegal gambling. Always has been, likely always will be. The three go hand, in hand, in hand.
As for your other points, yes. You never know who you could be fucking with via third party. Maybe that club owner already pays someone more powerful, maybe they're a criminal themselves. These are the risks we take as criminal RPers and often times we face consequence because of them. However, the knife cuts both ways. For instance, a guy at a club hit on my IC girlfriend and tried to pick her up. When I showed up, he insulted me and picked a fight. Not something wise to do against a character that's made in La Cosa Nostra. However, he didn't know. So he faced the consequences. That's life. But to say we should have some sort of IC policy to avoid club owners is just rather foolish, especially considering we are well aware they are the biggest money makers IG.
The mob still has major control in 2019. Indeed, unlike how their control used to be twenty or thirty years ago but still power none the less. In fact, part of the reason it has dwindled over the years is due to their own members turning state witness and the uprising of Eurasian OC which has posed a larger threat. We're based in a fictional city (Los Santos). If nobody is challenging us IG, and our members aren't flipping, why should we pretend to not have power when we do? We're in a position we're in because we have solid relationships IG that allow us to flourish. You can't just say that because the Colombo family in New York isn't what it used to be that we should have to act as if we're facing the same hard times. Many of us act behind the scenes and in the shadows, but there are still individuals just like in real life who are a bit more flashy and open about what they do. Again, it's an IC issue.
And then you go on to say well, protection rackets actually do exist. Okay which is it? They do or don't? Do a bit of research and show me some sources that actually say extortion is extinct. It's not, case and point.