What's "serious" here?

Even ignoring USB 3, most servers should work fine when capped to 100 or 200Mbps.

USB 3.1 over a USB port shouldn't be a bottleneck. You just need an adapter that suits the need.

What phones have USB 3? Almost all phones still do USB 2. It's not about the port (USB-C), it's what the host I/O is capable of.

The initial crop of USB-C adoption was mostly USB 2.0, but almost everyone has been USB 3+ for a long, long time now. All the Pixel phones except the 3a are USB 3 or higher, for example. And for comparison Samsung has been using 3.1 since the Galaxy S10e.

I just checked my Pixel 5 for example reports USB 3.2 (as in, that's what it's actually connecting as to a Linux host per bcdUSB)

What about actual transfer speeds? The signaling protocol gives the max speed. If something is I/O bottlenecked inside the phone it's still slow.