If you do need to drive 100 MB/s continuously, then Provisioned Throughput at the price that you mention would be appropriate. But note that you get 50 MB/s of throughput included with every TB of storage, and you only pay for the provisioned throughput in excess of what's included in your storage.
From a systems viewpoint, I can’t understand if there’s an actual technical challenge involved or if this pricing is just a lack of competitive pressure. Is there some corner case about the POSIX guarantees of EFS that makes higher throughput challenging to achieve?
(Otherwise one could just spray file blocks across many servers and maintain a metadata mapping of file to blocks to achieve good throughput)
It's not best tailored for the type of concurrent access that DBs will throw at it.
EFS is replicated across multiple AZs.
EFS supports multiple clientes, as opposed to one on EBS.
While technically true, the gap isn't large and it has enormous caveats. EFS can scale to a "whopping" 5x the aggregate throughput of a single gp3 EBS volume (5GB/sec EFS vs. 1GB/sec gp3). It requires at least 10 clients to reach that aggregate throughput. It barely beats a single io2 Block Express EBS volume (5GB/sec EFS vs. 4GB/sec io2 BE), and the io2 Block Express volume can do it with a single client. Reaching that 5GB/sec with EFS costs $30,000/month for either 100TB of data or 5GB/sec in provisioned bandwidth. Good luck!