I set up 2 CRS305 switches a few years ago and I recall testing file transfers then and I was getting 800-900MBs with large VM files.
Not sure if it was the cause but a few weeks ago I upgraded to the newest RouterOS firmware.
While still in the RouterOS I also upgraded the RouterBOARD fireware to 6.49.7.
I've tried switching to the switch SwOS and updated the SwOS version to 2.13 but it did not help.
Not sure if it means anything but the main switch got stuck a few times when switching to the SwOS. Power cycle did not work. I had the same IP address in both configs but ended up using the reset button after the power was back. It did the same thing when trying to update the SwOS firmware. ???
I have a simple setup with a few workstations and a laptop. They have very fast SSDs that can copy to each other in the same workstation at around 4000-5000MBs and to themselves at around1000-2000MBs.
I used the /int bridge port print command and all the ports have HW hardware on.