For these large scale infrastructures, they typically use JBOD, i.e. no RAID whatsoever and they achieve redundancy by maintaining multiple copies of the data over multiple disks spread around the datacentre. So it's not hardware RAID that requires a certain response time (I suspect the drives mentioned here drop because they timeout as it take a long time to random write on an SMR disk), more like a distributed software RAID. I think they likely also have their own file system so they are not dependent on a fixed block size, which allows them to save space if they have loads of small files.

RAID only protects you from disk failures, not machine failures. If you want to protect against machine failures (whole server offline), which might be an availability concern, then you would naturally want to replicate the data at a higher level. Once you’re doing that, it makes sense to only replicate the data at a higher level, because for a given level of safety, it is more efficient to replicate the data once, in one layer, than to replicate the data multiple times, at multiple layers.

RAID is only effective for workloads small enough that you care about a single machine.

It's a similar idea but they distribute the copies between machines, not just across disks in the same machine. https://www.backblaze.com/blog/reed-solomon/ So the drives in each box are not in a RAID configuration.