I don't think they'd ever admit that filesystem performance was an issue (though we all know it is; NTFS is over 30 years old!).
ext2, which is forwards compatible with ext3 and ext4, is slightly older than NTFS
A lot of the weirdly bad performance comes from all of the machinery that Windows wraps around file access for things like filter drivers. As long as you don't, say, indiscriminately follow every CreateFile() with a CloseHandle() and instead treat handle closure like garbage collection, you can actually eke out pretty good performance.
That all said, yeah, Windows containers are less than great for what I'd argue is one strikingly glaring flaw: Docker container images are built from smss.exe upward. That makes them not immediately portable between ntoskrnl.exe releases.
There are costs to it, in the form of architectural baggage and slower iteration, but what windows brings to the table is a deck swept mostly clear of footguns. That can give you a different form of robustness.
But SQL Server is in the unique position of being able to optimize Windows for their own needs. So they shouldn't have this kind of problem.
When NTFS came out it was way better than anything on Linux. Heck even in 2006 NTFS was better.
But Linux keeps getting new file systems while Windows keeps NTFS.
And no, it didn't perform better at NT4, XP, or Win7 times.