It's not improbable or impossible to find a way to make a 5-10% profit reliably.
You are correct, if you're talking about yearly profit. Even real (inflation-adjusted) profit for a limited (but arguably even very high) amount of capital can be "reliably" over 5% annually.
"Reliably" is in quotes because there is always a non-negligible risk. But, yeah, absent systemic crises it is not inconceivable that someone could make that kind of profit for decades without failure.
5% weekly can work for some amount of money and for some amount of time, and it's never reliable unless we talk about trivially small amounts. Even if someone has this kind of real world business (I think drug trafficking can sometimes achieve these kinds of returns), it will eventually grow large enough to saturate its market (hence lower profits) and attract competition (hence lower profits too).
This thread is a caricature of a ponzi scheme. Maybe, with enough idiots, it can grow to a real ponzi scheme.