On the other hand, I also came across posts where people were saying SD card read speeds on Android are just generally bad, especially on more recent versions were they are hampered by some kind of new file access system.
This is correct as far as I know (for android 10+). I ran into it with an open source maps app a while back and read up. Google intentionally kneecapped (and in later versions I thought almost eliminated) micro sd file access APIs for apps. For "security" reasons (not entirely junk but not entirely honest either) but it does just happen to align really well with their goal of forcing everyone to put everything in their cloud storage and access media by streaming not local storage
linkety: https://osmand.net/docs/user/troubleshooting/maps-data/