I am well aware that flash is overprovisioned. One consumer SSDs the overprovisioning is quite small (maybe 5-10%), so short stroking the SSD will have a much greater effect than on enterprise SSDs. It also has the nice side effect of giving the drive more free space to work with which allows the garbage collection room to be more gradual and efficient, which can improve performance for more write intensive workloads.

Actually, many storage arrays use battery backed RAM, not flash as a write buffer. Flash does not have the endurance needed to serve as the write buffer for a large storage array. Some products that use battery backed RAM for this purpose will dump the contents of that RAM onto flash. I worked on a messaging appliance that used that approach, albeit with supercaps to provide the hardware time to dump 4GB of DRAM onto a compact flash card. Supercaps were easier to monitor and maintain. There are also plenty of hardware RAID cards that use batteries for their write buffer as well.

Edit: there are also persistent memories like MRAM that don't need power to retain their contents which are used in this space as well.