A NVMe disk write is 20 microseconds.

I'm not sure if you're going out of your way to be a dick or just obtuse but 1) that's not true on most SSDs, 2) there's overhead with all the indirection on a Digital Ocean droplet, and 3) this is obviously a straight forward user space implementation that's going to have all kinds of scheduler overhead. I'm not sure who it's for but it seems to make some reasonable trades for simplicity.