[aleph_minus_one]

> You can't say "the system is actually really fast, it's just the OS that's slow", because the end result is just plain "the system is slow."

If performance is so critical, people do find ways around this. Just to give an arbitrary example since you mention file systems:

Oracle implemented their own filesystem (ASM Cluster File System (ACFS)):

> https://en.wikipedia.org/w/index.php?title=Oracle_Cloud_File...

"ACFS provides direct I/O for Oracle database I/O workloads. ACFS implements indirect I/O however for general purpose files that typically perform small I/O for better response time."