Technically battery-backed RAID is often compelling. But, Operationally such systems are super complex / expensive

I think that another important point is that writing to a RAID array write-back cache is very fast, because the application regains control as soon as the data is written in RAID’s memory. Of course this requires a battery-backed RAID, or at least capacitors, to ensure that data is preserved in the cache in case of a power outage. As long as writes are not bigger than the cache, this is very fast.
A drawback is that some learning cycle is needed, to periodically check the status of the battery, and this can heavily affect performance – but you can schedule your learning cycles when the workload is low.