The reason why this is useful is for DeFi applications that are blockchain native. If an applications needs to rely on the economic data, it will be able to use it natively without using an oracle. This doesn't improve the integrity of the data or replace the old ways of getting the data, just makes it more accessible to the blockchain ecosystem.
You're missing the point. A database or a normal http API is great if you're accessing the data from outside a blockchain. If you want smart contracts to access the data, it's better if the data is available natively inside the blockchain. You're probably not interested in smart contract, but there are other people that are trying to build smart contracts which use that data. One simple example would be a prediction market.
So... how is it useful? You're trading one oracle for another. Either of these oracles can be manipulated or compromised.
I think one could argue that it's more elegant from the point of view of blockchain maximalism. But I don't quite understand the utility in any other sense.
