It is not ridiculous. SD slot is much slower than the built-in NAND. iPhone SSD read speeds are about 1200 MB/sec, about 500 MB/sec write. The OS is optimized to take advantage of that fast, contiguous, and reliable memory.
Sequential, 512 MB test size, 65536 test count.
Similar to the lightning cable, generates an artificial market. Making design choices against the best interests of the customer. Not sure why anyone would be Ok w that. Restricting users options, taking advantage really