I don't think the problem is necessarily space, but rather write-limits being used by superfluous logging
Its a shame mobile devices don't have a SMART equivalent, would be nice to have some warning as something approaches the end of its life.
It’s not going to write at twice the rate just because more space is available.
You can find out a bit more here https://www.seagate.com/gb/en/blog/ssd-over-provisioning-and...
I also remember a guide a while ago on how to reprogram a SSD to operate in SLC mode instead of MLC. You lost disk capacity but gained a large performance boost and a reduced error rate.