If you have fastboot your device is not really bricked. So if you want to get back to a good base you should be able to flash an Oxygen “fastboot ROM”. As explained in the above links “fastboot ROMs” are not archived by OnePlus officially, but can usually be found from the links I gave.
YouTube spoiler
… or as a video https://www.youtube.com/watch?v=An5VQViUDb4
When we take the wrong turns this is the expected behaviour if system fails the device falls back to recovery if recovery fails the device falls back to fastboot … but one important detail to check though … you say
I have to reboot into bootloader
At this point what is the response to
fastboot devices
Notice in this thread Oneplus Nord manual installation problems we spent a long time to establish if we were actually talking about fastbootd – fastboot D. The thread does have a successful resolution though 
Is your device the Nord avicii, Info about OnePlus Nord - avicii ? and which model ?
Models Supported
AC2001(India)
AC2003(EU)
Other models are not supported
This thread OnePlus - Nord - avicci - Documentation Suggestions may help to explain difficulties experienced.