Earlier quoted context omitted.
Is it possible to determine which sectors are physically sequential given remapping for wear-leveling? Otherwise the claimed defragmentation here is not actually resulting in sequential data.
You cannot directly inspect the degree of fragmentation, because it has less to do with being contiguous in the Logical Block Address (LBA) space and more to do with having been written at the same time. To properly defragment a file on a SSD, you pretty much need to sequentially re-write the whole file in one go, to a newly-allocated part of the drive's LBA space.
Which is rather a case for home use, not practical for highly parallel access industrial use cases. That's why the issue became a research topic. For the first time I saw a proof that the "fact" SSDs do not need defragmentation is actually a myth. Well, you still want to avoid explicit defragmentation (waste of time and SSD lifetime) by filesystem driver submitting additional hints (using new NVMe extensions) to the SSD controller about what blocks belong to the same file, so that SSD can place them for an optimal sequential access with properly interleaving (not necessary strictly physically consecutively whatever this means on SSD).