It’s definitely disappointing, and I hit the same problem–I really enjoyed the original HiFive1 w/ Arduino and got this expecting it to work the same.
…they do also have a bare JTAG header on the board, I wonder if one could use an FTDI jtag<->usb adapter and fake it being an original HiFive?
I have had [mixed] results with the USB mass storage, and the RevB platform wise should be very similar to original. Maybe you could verify/compile your stuff in Arduino against the HiFive1, take the elf and convert to a hex file (elf2hex should be in freedom-e-sdk), then drag-n-drop to the board? It’s not great, but it may be workable.
I’m currently experimenting to get OpenOCD working with my board and I’m slowly making some progress, but I’m not sure how much functionality I’ll be able to get out of it.