I think you're "begging the question." You believe that Tether is a fraud. You're using the fact that the price on a CEX and DEX are the same to justify that belief. "See, the price on a DEX matches that on a CEX, therefore Tether is a fraud."

Whether or not Tether is a fraud has nothing to do with the price match on a CEX and DEX. The price on CEXs and DEXs will always match due to arbitrage.

(This isn't a statement on whether or not Tether is a fraud. I'm just pointing out that the price on a CEX and DEX will always match with sufficient liquidity in the market).