Most martial artists living and teaching today have not tested their martial arts styles or systems in actual combative situations, where they were defending themselves against someone actually trying to hurt or kill them.
This is not actually that bad of a thing, overall, if you think about it. But it really means that the true effectiveness of what we train – and that would include most styles – is unknown, because it’s always possible that Person A trained in, say, taekwondo, will survive a self-defense scenario, and Person B, trained identically and in a similar situation, won’t surive.
It’s not possible to predict for each individual whether or not their martial arts training is “effective” until the time comes to test it for real. And even then, it might not be the style, it may just be the individual or the circumstances.
Me, personally, I don’t want to find out. I like a peaceful life!
That being said, there are a few “fake” styles out there, that have been demonstrated as something that doesn’t work OR comes from a made-up history or lineage. Yellow Bamboo is one that comes to mind, another is EFO (Empty Force). I would also advise avoid training with anyone who claims a secret ninja teacher started training them at age 3 in US suburbs and can’t prove said teacher ever existed independently and they don’t actually know their real name. And I would avoid any style that claims to have “secrets” above a certain level that they can’t/won’t show the public because they’re too “dangerous” (my alarm bells go off when I hear this).
But here’s something to keep in mind:
A lot of the “this style is fake” and “that style is not fake” is really just braggadocio. “Of course Aikido is bullshit” says the MMA guy, never mind that cop over there who’s used what she’s learned in that style on the streets for 30 years as a beat cop. “BJJ is useless for self defense” says the karateka, never mind that highly ranked BJJ player who dealt with an attacker on the streets.
For every claim about XYZ style won’t work in “the street”, there’s an example of it working at least once, on video. Who knows how many times it worked off-camera.
Each of us says that our style is best, and those guys over there are fakes and frauds and ineffective, because that’s one way we justify to ourselves the decision we made to pick the style we study in the first place. So keep that in mind.
So my advice is this: focus on a martial art you enjoy, that has training that includes working against resisting opponents, and seems to fit your point of view best.