Regulation won't be a silver bullet, plenty of scams remain in regulated finance that they are supposed to fix as well.
No regulator in the world has successfully stopped a scam before people lost money (afaik). But if you establish some regulatory framework in which people have to disclose information, establishes capital rules, etc. then it makes that less likely.
Scams are a central component of financial innovation. But this specific kind of scam (stealing money from customers) is basically non-existent at scale today because of regulation.
It's impossible to prove anyone stopping anything before harms materialize because the prevented harms never happened. Regulators have definitely stopped scams early enough to reimburse victims. And where they couldn't (and where regulators were the ones to stop it) would have presumably kept going absent their interference. Americans are to a large degree shielded from FTX's collapse on account of regulation.
Just trade on chain. Smart contracts are transparent by default.