Arc's privacy is not the first TEE secret-sharing idea. Also it's not implemented yet, but announced four times...
For Confidential stablecoin transfers specifically, cryptography is scalable and compliant without relying on a bunch of TEEs, TFHE, or threshold decryption.
I got asked about Arc's "privacy" proposal:
1)its not private and I hope they don't say it is. A private zone is a TEE, ran by an admin, who sees and controls everything.
2) These ideas aren't knew, but a promising integration of them is great.
3) We can get better privacy.