You're kinda telling people to waste time. It is not a myth.

League, rating scale, etc. are a measurement that's made from the outside. Not internally. Everyone wants to date the best that they can date. A fit muscular guy is likely going to garner more attention from more people than a fat guy. That is a fact. Subjectivity in attraction certainly exists, but it's not that widely swinging. A very few curve extremely outside of the norm (i.e fetish). For example, almost every person attracted to a male would find Brad Pitt very attractive. Etc.

So if you go after the attractive person, they're also going to get many alternate options. And they're going to pick someone they find most attractive among their suitors. If I had 100 matches on a dating app for example, I'm only going to bother spending my time talking to 10 of them and ghost the 90. I just can't deal with the rest, humans only have so much time. If I get 1000 matches, I'm going to ignore 990 of them. My criteria in picking who is most attractive is likely not that much different from anyone else.

Question of if they're out of their league means are you in the ignore pile, or the talk to pile, and sometimes the friendzone pile (i.e. you're the backup). You can try to claw your way out of the ghosted, but your chances are slim. So it's better use of your time and resources to retarget to another lower tier person who might only get 20 matches and will bother talking to 10 people. If that still doesn't work, you keep going lower. This is effectively how the "dating marketplace" puts values on people.

You can keep trying to date the higher tier people, but you'll keep getting outright rejected or not have a long term relationship with them. Because they know they can do better because they'll keep getting suitors throughout their life.

World was certainly easier to date in the era of pre-dating apps or social media. Since the pool of people around each other is a lot smaller. But thanks to online interactions, we're literally competing against countless others. So, it's better to not waste your time on someone out of your league. You aren't going to keep them. All you did is waste time (and probably lot of money if you're a guy, and that money is going to be proportional to the gap between your leagues).