I opened WBTC's contract myself (block 25445276) and traced every permission to a single owner address — one key that can mint more supply and pause every transfer on the asset. Whether a custodian's trust comes from a banking license or a technology network, on-chain it converges to the same thing: one key, held by someone. With ~84% of U.S. spot Bitcoin ETF assets custodied at Coinbase alone, that's a systemic concentration risk hiding behind the word "custody."