It even let traders know how useless stop loss can be.
Stop-loss is designed to make trading gambling earning the exchange house edge that keeps trader losing to the house.
This is a very wrong description of stop loss. The issue is that many are trading, but most are not real traders, which is why losing due to stop loss is a big deal, as it's the evil, no; most people's ideology about it are merely wrong, and many people place it anyhow.
Stop loss is not mainly designed to protect that position it cut short, it was actually designed to protect your trading account. But most traders are not patient, which is more reason they can't be successful in trading. Besides, there's no way you can practice a quality risk management without needing your stop loss, and if your strategy is good, you would praise your stop loss because it will will effectively lock the 1 in the ratio part of your R:R, which is actually it's beautiful. It's what I do everyday.