Basically, I have the same problems as everyone else: delete out ST from GH, and phantom ST devices still show up in the list of Home control devices, but ST doesn’t show up in the account list.
If you go to GH->Account->Settings->Services->Explore and type in SmartThings, no matter how many times you click “Unlink” and it says “Unlink successful,” every time you restart the Google Assistant app, it has the button as “Unlink” because IT ALWAYS THINKS ITS LINKED.
I’ve learned a few things:
A. Having two accounts using ST and being a pre-Samsung acct user would describe me. My wife has her own Google and own ST account, and she has zero issues linking things and making them work, but I still see phantom devices no matter what in the “Assistant->Home control” area.
B. It’s definitely related to my Google account, not to ST.
C. Google end-user support is not capable/talented enough to fix this.
D. It’s some sort of server-side cache issue. No amount of deleting/restarting/etc. issues will cause it to flip.
E. Even turning off “SmartThings remembering me” or deleting SmartThings out of myaccount.google.com at the linked accounts section has zero effect on the legacy Home control devices showing up in Google Assistant.