SD cards are made for cameras etc, and they're good for that. They have sequential RW speeds to match common video formats at 1X speed or burst photo capture. The spec sheets won't tell you how terrible the random write speed is, and even the quoted sequential speeds aren't very good, but that's ok for cameras.
I use a modern high-end SD card from SanDisk as semi-permanent storage in my MBP. If I copy anything to that card that's not a single file, it takes forever. Overall it feels worse than using an old HDD. I have to actually think about what I store on it (mostly videos/photos), so I totally see the reason for wanting more internal storage instead of an SD slot.
That's only sequential write speed. Of course the camera features on a phone will have no problem using an SD card, but other stuff dealing with more random writes to things like SQLite stores (common for phone apps) or directory trees might. Like I said, I've only used an SD card on my Mac, and it was a bad experience, so I'm guessing a bit about phone usage.
With a decent filesystem and a ram buffer the better microsd cards still beat an old 5400rpm 128GB HDD's sequential speed when doing random writes of ~500kB files by a fair margin.
150MB/s is nowhere near SSD speed, but it would saturate a SATA I port.
I'm not sure about that test cause there are too many variables, but in the typical real-world usage of like cloning a git code repo onto my SD card or opening a zip file, it was always painfully slow. I wasn't even benchmarking, I was just trying to get stuff done and not wanting to wait on it. In fact I moved the files to an HDD to do it one time.
Considering 100 GB HDD's came out 20+ years ago that's not very suprising. If people are comparing SD cards to HDD's they're probably comparing to HDD's made in the last 10 years.
OP specifically cited an old hdd in the pre-ssd days. New HDDs are still at best on par with a high end microsd used as internal storage (compare an A2 microsd 'rated' at 2000 but actually getting about 800 iops vs a high end hdd benchmarking at 200-300).
Mounting without a buffer on a badly chosen filesystem in what could well be the M1's abysmally slow sd reader isn't a representative test.
Hare braned formatting tools will also often offset the filesystem by 512 Bytes (necessitating two writes and two reads for one 4k write) or use blocks that aren't 4kiB
FWIW my MacBook Pro is the 2015 Intel version, and my card is HFS+ formatted (Android would use FAT32 or Ext4). I got similar performance with an external USB reader IIRC, but maybe it's time to test again.
USB 2 has very poor latency for this use case and the sd connector lacks the pins for newer sd cards.
A usb 3 UHS III reader would be able to talk to the card at full speed, then it's a matter of convincing the OS to trim it and buffer as if it's an internal hdd. Kinda expensive and pointless to go to that effort to get 2x hdd performance when there are NVME enclosures for cheaper SSDs that have 100x the IOPs though.
I use a modern high-end SD card from SanDisk as semi-permanent storage in my MBP. If I copy anything to that card that's not a single file, it takes forever. Overall it feels worse than using an old HDD. I have to actually think about what I store on it (mostly videos/photos), so I totally see the reason for wanting more internal storage instead of an SD slot.