[Razengan]

> despite the fact that 256GB of flash can be had for ~40GBP, the latest smartphones come with piffling amounts of storage and seemingly no expandable slots.

I'm sure there's different speeds and other variables to consider in flash storage, just as prices vary for RAM and just about everything else really. The exact tech in an SD card may not be suitable for your phone or tablet's permanent storage, and definitely not suitable for an SSD, otherwise everyone would be installing their OS on SD cards.