Even on my Mac (tested with 6 different readers, including one purporting A2 compatibility) the best microSD cards are abysmal for random access. But they do get closer to 90-120 MB/sec for reads, at least.
> To get advertised speeds on most of the cards, I am guessing you need to work for the SD association's marketing department
Note that there's all kinds of special, video camera-oriented things in the SD standard, where you can preallocate/pre-erase a big chunk to sequentially write, stream data in and do big commits. That's where you actually hit the rated speeds, because the flash controller is able to benefit from all the hinting.
Using SD with general purpose filesystem drivers, etc, is really just a very common edge case.
I believed you were writing about analysis linked in parent article (you know, the article we're all discussing), where he compares USB3.0 throughput to SD on the Raspberry Pi 4, and finds speed differences of 3-16x+:
Now I see that someone linked another article inbetween, which you beat up for being on 3B+, but the conclusions remain largely the same when tested on the 4. And note that these tests were without UASP on the USB drive, so USB was handicapped.
