Not exactly. After many, many decades of frauds, schemes, panics, and crashes, harsh experience has led to a regime where
nobody can do anything without a very explicit carve out. In tech terms, it's a default "deny all", with a white list of "things which are not thinly disguised ponzi schemes", not a default "allow all" with a black list of "things which have been shown to be thinly disguised ponzi schemes".
So yes, banks are one of the exemptions, because they have their own regulator (which is one way to get on the white list).
> Consulting with relevant regulators when the legislation is unclear (or non-existent) seems like the opposite of a red flag.
No, the red flag is that Coinbase (correctly!) understands that the SEC is the relevant regulator. Your local credit union does not go to the SEC when they want to offer a new type of savings account because the SEC does not regulate credit unions. Which is good, because the SEC is only competent to apply securities law, and securities law doesn't allow savings accounts.
So yes, absolutely you should consult with the relevant regulator, and if the relevant regulator for you is the Office of the Comptroller of the Currency (who regulate banks), they're probably going to cheerfully sign off on your savings account idea; they like savings accounts. But for Coinbase, it's not the relevant regulator, because they're not a bank. Nor do they seem to fall into any of the other many exceptions and regulatory schemes so...