As bad as their random-read performance is, their random-WRITE performance is usually much, MUCH worse.
You get a massive speed increase if you switch to a better filesystem: btrfs or f2fs.
git reset --hard: 3m45s btrfs, 3m55s f2fs, 12m30s ext4, 16-18m xfs (huge variance)
"./configure && make -j4 && make test" of a shit package with only ~2MB of persistent writes: f2fs 95s, btrfs 97s, xfs 120s, ext4 122s
(class-4 card in a Pine64)
And almost none do their own wear-leveling, so a Linux swapfile can literally max out the lifetime writes of a microSD card in 1-3 months
Not SD but eMMC: Samsung's fancy-schmancy eMMC cards are apparently made by someone no one told about the write endurance problem: I've been running Debian archive rebuilds and other I/O-heavy loads since early 2013 on a 64GB card ($89) in an Odroid-U2, and despite me heavily overcommitting memory (ie, heavy swapping a lot of the time), the card is still going strong.