For comparison, a 32GB Sandisk Extreme Pro 95MB/s MicroSD, a 32GB Samsung EVO+ MicroSD and the Orange Pi PC Plus eMMC speeds:
(using 'iozone -e -I -a -s 100M -r 4k -r 16k -r 512k -r 1024k -r 16384k -i 0 -i 1 -i 2')
32GB Sandisk Extreme Pro 95MB/s MicroSD
random random bkwd record stride
kB reclen write rewrite read reread read write read rewrite read fwrite frewrite fread frer ead
102400 4 2891 2973 8610 8609 8378 4764
102400 16 7914 8058 16077 16097 16064 11118
102400 512 20219 20331 21772 21724 21764 19582
102400 1024 20450 20479 22279 22277 22269 20117
102400 16384 21585 21620 22957 22967 22956 21358
32GB Samsung EVO+ MicroSD
random random bkwd record stride
kB reclen write rewrite read reread read write read rewrite read fwrite frewrite fread frer ead
102400 4 1510 2426 7017 7380 7496 3326
102400 16 10629 11033 14575 14563 14579 11048
102400 512 20020 20167 21592 21594 21584 20095
102400 1024 20283 20370 22130 22129 22128 20340
102400 16384 21053 21198 22906 22905 22903 21190
Orange Pi PC Plus eMMC
random random bkwd record stride
kB reclen write rewrite read reread read write read rewrite read fwrite frewrite fread frer ead
102400 4 6204 6558 15817 15812 13358 6422
102400 16 21499 22650 38919 38938 34894 21409
102400 512 35602 35566 64903 64908 64912 34244
102400 1024 36147 36359 69756 70083 69976 35780
102400 16384 38198 38697 78658 78768 78775 38495
MicroSD clearly bottlenecks (particularly obvious with one of the fastest UHS-1 MicroSD cards in the Extreme Pro) and eMMC is definitely the better option for OS by the looks.