It's the other way around, actually. Having small set of authorities that reach consensus via raft/pbft in case of quorum means that ethereum blockchain can be much faster. You still have full transparency of what's happening, you have access to the chain, you can read it, validate it, etc. They just run minting of blocks for you. It's true that if they don't like you, they can refuse to include transactions from you for example - that's the main cons from public consensus like PoW. But they are not worried about it, of course and other participants are usually not worried as well because they know that whoever controls minting nodes have strong incentives to run it fair (otherwise participants would not give a shit to join it). This is different from public chains where those rules don't exist. In big corps integration and security is a massive problem. Blockchain reduces those two problems by orders of magnitude. If you wanted to "implement it by any random database system" - you'd end up with something like ethereum. You can't just spawn your public postgres and publish public api to create new users, can you? Quorum has also some other extensions to ethereum related to privacy (private contracts, anonymity etc) that are attractive to corporations. It's nice to see them open sourcing quorum and publishing something real-world based on it.