Show me the SD card that can saturate USB 3 or USB C. The fastest sony cards top out at about 300Mbps. Heck, USB 2 could handle that at top speed (theoretically; most implementations stunk). USB C is better with really high bandwidth things like eGPU, 4k displays, etc., but sd cards are not the best argument to make here.

The fastest SD cards are 300 megabytes/second, not megabit. All my Sandisk Extreme Pro cards, for example. I also have a bunch of Extreme Pro CF cards that are 160MB/s.

And then there's CFast - speeds in the 400MB/s range.

Apologies, I messed up my capitalization. That ought to have been "MB". You're right that things like compact flash are faster, but USB 3 has can handle over 600 MB per second.

Right, but modern cards can certainly saturate USB 2.0 easily.

you still need the card to support that speed though...

I'd imagine the card reader and USB are the same speed, unless they screwed up the implementation of the reader

Still not sure I understand what you mean. If you have a slower USB, slower card reader, or slower card, all components are bound by that speed. The USB 3 supports a much faster than the card speed; I'm guessing most readers are similar speed. The cards themselves are the limiting factor here.

Perhaps he's alluding to the fact that a lot of laptops have had USB2 card readers internally but USB 3 ports going out.