I just checked my phone and the up/down speed for files is roughly 40MB/s despite having a USB 3 connection.

USB 2 has a max. transfer rate (under optimal conditions) of 60MB/s, so I think when the phone storage improves a bit or the cable is a bit longer it will likely become a bottleneck.

Also note that there are other applications than transfering files which might need more bandwidth.

To be fair it really doesn’t make much of a difference but USB 3 is now the standard for a century and has been around since 2008 so I somewhere expect a 600€ phone to alsl have it.