They described what they are doing in their documentation, but the core ethical problem here is that the only users that would use their service are those incapable of understanding how UST/Terra worked, because anyone capable of understanding would just deposit funds directly and get higher APR for the same risk! Extremely predatory.
UST fooled many ...not very bright people who genuinely didn't realize it's a ponzi scheme - but obviously smart and technically proficient founders of Stablegains' have no such excuse. Zero room for doubt - they fully knew it's certain to collapse eventually, banking on their legal terms to protect them from liability while privately profiting as long as it works.
Founders of Stablegains belong in prison and everything they own should be confiscated and divided among victims. Sadly they are probably safe - as knowing the inevitability of collapse they must have felt their legalese to be ironclad.
I'm not saying these aren't some other kind of scam but lots of people use "Ponzi" as if it meant any kind of scam... And generally speaking "how many thingy-coins do I own" is the one thing cryptocurrencies focus on making very difficult.
TLDR: Everybody overuses "Ponzi" and it annoys me.