I think syncing to the network is a good idea (and I’m aware that it’s not a new idea). Supposing you want to ensure that some transaction is committed to disk, you have to wait for fsync. Fsync is much slower than a LAN ping or even internet pings within a single country, if you are well connected. (e.g. ping from my pi.nipl.net -> hu.nipl.net appears to average about 0.001 ms).
If you store your transactions on several remote servers, your reliability is much greater. Even if the main server suddenly explodes or catches fire, you still have a record of all the committed transactions. RAID provides no such guarantees. It’s extremely unusual for 3 servers in different datacenters to explode simultaneously – if it’s a concern, get more servers.