As it is generally accepted (by me, anyway) that "HYIP" is a synonym for Ponzi scheme, despite a recent change in the law such schemes are not illegal in Russia (indeed, thanks to Sergey Panteleevich RIP, they can be seen as an historical part of Russia's rich financial culture).
What I'm trying to say, without in any way supporting these schemes, is that they don't pretend to be anything else.
In order to fulfill Western criteria for a true Ponzi (and for me to support a forum flag against them), I believe there must be some deceptive element involved, certainly more than just an absurd ROI and no claimed source of income other than new investment.
But that's just my opinion and I know it's not shared universally.
I also did not change my mind:
Yes, you rightly wrote that the activities of Mavrodi at that time were not prohibited. But in 2017, a law came into force in Russia prohibiting the collection of funds in financial pyramids. This law prohibits the distribution of advertising in the media and the Internet about the attractiveness of such financial schemes. For violators, this law provides a fine of up to $ 15,000.
The deception is that investors are offered unrealistic returns.