ItsI wouldn't say that it's completely irrelevant. This means that mounting, reading and writing of the USB drive in general is working.
Whats also working is setting the SMB1 server working dir to /storage/emulated/0. Then the share is not empty. So the SMB1 server is working properly.
Whats not working is using an usb drive as working dir.
smb://[server]/[share]. SHARE the location, and then you can access it using SMB and even via 127.0.0.1 or whatever. I personally have found that you have not clearly explained exactly what you are trying to achieve as your end goal amongst the confusion of your claims.
As for FTP being relevant, you missed the point and its simply argumentative. SMB & FTP are two different protocols, so their parameters/config can be expected to be different; hence I said it was irrelevant. I tried to help. I'm out, hopefully someone else will take their time to help you.