MakerDAO is not decentralised, simply because the ETH/USD price feed isn't decentralised. If the servers providing the feed get hacked, say goodbye to your ETH collateral.
Stakeholder vote elects a smart contract that takes the median of dozens of price feeds controlled by various independent parties, so it's decentralized to some extent, and decentralization is not a clear-cut binary attribute.
That's just "decentralization" by obscurity. (emphasis on the quotes)
That aside, the main problem isn't centralization but rather the trust level. The point is to not have to trust someone isn't serving you the false data. Contracts must be created and ran only when the data can be cryptographically verified to be true.
There are no trustless oracles if any of the required data are outside of the settlement system (e.x. blockchain). Even when the data are inside, you still have cases of collusion that make things problematic.
People are trying to sell something that's close to impossible. Especially when they try to add infinite flexibility on it.
Even with the currently low stakes there have been incidents of "oracles" getting compromised. There are several strategies to try and camouflage a centralized oracle to a faux decentralized entity but eventually if stakes get high enough, your entity will become a target and it'll become once again obvious what's happening.