The DIMMs were their own shitshow and I don't know how they even made it as far as they did.

The SSDs were never going to be dominant at straight read or write workloads, but they were absolutely king of the hill at mixed workloads because, as you note, time to first byte was so low that they switched between read and write faster than anything short of DRAM. This was really, really useful for a lot of workloads, but benchmarkers rarely bothered to look at this corner... despite it being, say, the exact workload of an OS boot drive.

For years there was nothing that could touch them in that corner (OS drive, swap drive, etc) and to this day it's unclear if the best modern drives still can or can't compete.

It sounds like they didn't do a good job of putting the DIMM version in the hands of folks who'd write the drivers just for fun.

The read path is sort of a wash, but writes are still unequalled. NAND writes feel like you're mailing a letter to the floating gate...