So since RenBTC is not a real bridge and WBTC is centralized due to BitGo, the only safe way to do this would be to immediately sell the wBTC for ETH and hold that on the ETH chain? Or some other stablecoin?
Nothing has changed, there is still one point of failure. It is true that in the case of CEX, the probability of failure is greater, as your account can be frozen or identity verification may be requested, but all current bridges require trust in them, trust that there is no vulnerable when locking your bitcoin and that there is enough From the liquidity to sell WBTC, here if there is not enough liquidity, you may sell WBTC at less than its price.
Why not try P2P DEX like bisq It's decentralized, and you have many options so you won't have to worry about liquidity.
Cryptocurrency bridges are not good enough in their security and many bridges were hacked. They are vulnerable to hacks and I won't take risk with cryptocurrency bridges if I have other options.
it is not easy to find vulnerable in bridges. In most cases, it is insider attack or an employee who left development.